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Impact of differences in speciation of organic compounds in wastewater from large WWTPs on technological parameters, economic efficiency and modelling of chemically assisted primary sedimentation process
Abstract
The aim of the study was to supplement the information missing in the literature on the influence of organic compounds speciation (percentage of chemical oxygen demand (COD) fractions, readily biodegradable and non–biodegradable dissolved organic matter; slowly biodegradable and non‒biodegradable insoluble organic matter ) in wastewater on chemically assisted primary sedimentation process and its potential impact on the energy and economic balance of the plant. The statistical modelling of the chemically assisted primary sedimentation process using artificial neural networks (ANN) was a novelty. It was also important to check the differences resulting from the use of coagulants, polyelectolites and their doses. For both large wastewater treatment plants (>500,000 people equivalent) located in the various regions of the country in Central Europe only ferric chloride had a positive balance. The addition of polyelectrolyte in the Wroclaw wastewater did not affect the chemically assisted primary sedimentation process but in the Bialystok wastewater it strengthened the process effect. In both plants only doses from 10 to 40 mgFe/dm³ are cost-effective. The results indicate that the addition of polyelectrolyte should be taken into account in this application and was correlated with the amount of colloidal COD fractions in wastewater. The developed ANN models reflected well the effectiveness of COD removal in both large WWTP while the sensitivity analysis of individual ANN models showed differences in the variables affecting the calculation process of both models, despite similar values of parameters characterizing wastewater in both wastewater treatment plants.
... Before entering the water bodies, discharged wastewater goes through disinfection process. The most common methods include the use of gaseous chlorine, UV disinfection or ozonation [19][20][21][22][23]. The point for the potential biogas project applications is presented at Figure 1. ...
... Protozoa grazing plays an important role in decay or endogenous respiration [18] and as such it is considered one of its component. Despite this simplification, ASM models have proved to be an excellent tool when modelling and forecasting the activated sludge process [33]. Considering these interactions, in systems where efficient biomass flocculation in not necessary (i.e. ...
One of the key technological parameters for highly efficient wastewater treatment methods is bacterial mortality. Protozoa are known for feeding on free floating bacteria, that initiate floc formation and participate in putrefaction process. Reliable protozoa removal methods are still unavailable which have negative impact on the development of the current knowledge in this field. The aim of this study was to find the most effective method which removes most of protozoa present in the activated sludge without affecting the overall treatment efficiency. Seven possible methods of removing protozoa were tested by analysing several technological parameters. The evaluation of the presented methods was based on the efficiency of protozoa removal, as well as on the effects of the removal methods on autotrophic, heterotrophic and endogenous oxygen uptake. Mechanical disintegration proved to be the most effective and reliable method. It allowed for the complete removal of protozoa without the inhibition or inactivation of bacteria. The comprehensive and complete data obtained from the conducted research will be used to improve existing wastewater treatment processes with regards to both the technological point of view and mathematical modelling.
... In practice, total Kjeldahl nitrogen is an environmental pollution indicator, and its control makes it possible to follow the evolution of contamination [28]. In our study, the TKN vitiated a lot throughout the investigation. ...
This study focuses on the physico-chemical properties of the Moroccan dairy industrial unit in various locations of the facility between 2014 and 2015. Also to confirm the significant level of pollution caused by the different activities of this industrial unit. Using adsorption on commercial activated carbon, the treatment of the dairy effluent of the facility in terms of chemical oxygen demand (COD) removal, suspended solids, and conductivity decrease. The results show that the dairy effluent is loaded with the organic matter with an average COD of 3,500 mg/L, total Kjeldahl nitrogen (TKN) with an average TKN-N: 45.35 mg/L, the total suspended solids (TSS) value for the main discharge is 460.214 mg/L. Daily monitoring of this physico-chemical characterization in the plant reveals significant values that greatly exceed the permissible limits of the Moroccan standard. Using the experimental design software for the commercial activated carbon treatment model showing p-values for TSS (p-values = 0.0397) and for COD and conductivity, the p-values are greater than 0.05 p-values (COD = 0.1167; p-values) (conductivity = 0.152). Analysis of variance showed that the R-squared coefficients for COD, TSS, and conductivity, R 2 (COD) = 1, R 2 (TSS) = 1, and R 2 (conductivity) = 0.99, respectively. Because the coefficient values are close to 1. In addition, the best conditions for adsorption of dairy wastewater by commercial activated carbon are adsorbent dose = 10 g/L, pH = 10, and T = 40°C.
... So, the BP algorithm is implemented to a training set, then the performance of the resulting input-output set is validated on different data, and, finally, a test set is considered so the real network performance can be measured (Pasini, 2015). The detail of ANN modeling process can be found elsewhere (Prabhu and Karthikeyan, 2018;Ranade et al., 2021;Struk-Sokolowska et al., 2020). ...
Anaerobic digestion (AD) is widely adopted for remediating diverse organic wastes with simultaneous production of renewable energy and nutrient-rich digestate. AD process, however, suffers from instability, thereby adversely affecting biogas production. There have been significant efforts in developing strategies to control the AD process to maintain process stability and predict AD performance. Among these strategies, machine learning (ML) has gained significant interest in recent years in AD process optimization, prediction of uncertain parameters, detection of perturbations, and real-time monitoring. ML uses inductive inference to generalize correlations between input and output data, subsequently used to make informed decisions in new circumstances. This review aims to critically examine ML as applied to the AD process and provides an in-depth assessment of important algorithms (ANN, ANFIS, SVM, RF, GA, and PSO) and their applications in AD modeling. The review also outlines some challenges and perspectives of ML, and highlights future research directions.
Increasing energy efficiency in wastewater treatment plants (WWTPs) is becoming more important. An emerging approach to addressing this issue is to exploit development in data science and modelling. Deployment of sensors to measure various parameters in WWTPs opens greater opportunities for exploiting the wealth of data. Artificial intelligence (AI) is emerging as a solution for automation and digitalization in the wastewater sector. This review aims to comprehensively investigate, summarize and analyze recent developments in AI methods applied to the modelling of WWTPs. The review shows that among the standalone models, Artificial Neural Networks (ANN) was the most popular model followed by, in descending order: Decision Trees (DT), Fuzzy Logic (FL), Genetic algorithm (GA) and Support Vector Machine (SVM). In the case of incomplete data, FL was the most frequently used method as it uses linguistic expert rules to find an approximation for the missing data. Regarding accuracy and precision, hybrid models demonstrated relatively better performance than the standalone ones. Among these models, the Machine Learning (ML)-metaheuristic, which integrates an AI model with a bioinspired optimization method, was the most preferred type as it was used in more than 45% of the hybrid models. Correlation coefficient (R), Correlation of Determination (R²) and Root Mean Square Error (RMSE) were the frequently used metrics for model performance evaluation. Finally, the review shows that despite recent developments, industrial deployment is still lacking. The industrial application requires close interaction of interested parties, among which research institutes, private sector and public sector play an inevitable role. The future research should focus on mitigating the barriers for more in-depth collaboration of interested parties and finding new paths for more cooperative and harmonized activity of them.
This study investigates whether a novel estimation method based on machine learning can feasibly predict the readily biodegradable chemical oxygen demand (RB-COD) and slowly biodegradable COD (SB-COD) in municipal wastewater from the oxidation–reduction potential (ORP) data of anoxic batch experiments. Anoxic batch experiments were conducted with highly mixed liquor volatile suspended solids under different RB-COD and SB-COD conditions. As the RB-COD increased, the ORP breakpoint appeared earlier, and fermentation occurred in the interior of the activated sludge, even under anoxic conditions. Therefore, the ORP decline rates before and after the breakpoint were significantly correlated with the RB-COD and SB-COD, respectively (p < 0.05). The two biodegradable CODs were estimated separately using six machine learning models: an artificial neural network (ANN), support vector regression (SVR), an ANN-based AdaBoost, a SVR-based AdaBoost, decision tree, and random forest. Against the ORP dataset, the RB-COD and SB-COD estimation correlation coefficients of SVR-based AdaBoost were 0.96 and 0.88, respectively. To identify which ORP data are useful for estimations, the ORP decline rates before and after the breakpoint were separately input as datasets to the estimation methods. All six machine learning models successfully estimated the two biodegradable CODs simultaneously with accuracies of ≥0.80 from only ORP time-series data. Sensitivity analysis using the Shapley additive explanation method demonstrated that the ORP decline rates before and after the breakpoint obviously contributed to the estimation of RB-COD and SB-COD, respectively, indicating that acquiring the ORP data with various decline rates before and after the breakpoint improved the estimations of RB-COD and SB-COD, respectively. This novel estimation method for RB-COD and SB-COD can assist the rapid control of biological wastewater treatment when the biodegradable organic matter concentration dynamically changes in influent wastewater.
A rapid, sensitive, economically and ecologically friendly method based on one-step ultrasound-assisted emulsification microextraction and in situ derivatization followed by gas chromatography–mass spectrometry for simultaneous determination of low molecular benzotriazoles and benzotriazole-based ultraviolet filters was developed. The optimized method allows quantification of benzotriazole, 4-methylbenzotriazole, 5-methylbenzotriazole; 5-chlorobenzotriazole, 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzortriazole and 2-(2′-hydroxy-5′-(1,1,3,3-tetramethylbutyl)phenyl)benzotriazole in municipal and industrial (dairy) wastewater. The method was validated using real influent and effluent wastewater and samples at various stages of the purification process. Relative recoveries obtained using wastewater as sample matrix were between 77 and 137%, method limits of detection from 0.001 to 0.035 µg/L, method limits of quantification from 0.003 to 0.116 µg/L, the repeatability expressed by the coefficient of variation did not exceed 12%. The use of the method for the determination of tested compounds in municipal and industrial wastewater showed their presence in most of the tested samples, in concentrations from LoD to 6.110 µg/L. The conducted studies of samples from municipal wastewater treatment plant located in north-east Poland showed that the effectiveness of benzotriazole removal by this plant wasfrom 29 to 84%. The load of tested compounds released into the environment by this facility ranges from 2 to 269 mg/day/1000 inhabitants.
Based on the calibrated model for an Anaerobic-Anoxic-Oxic (A²O) municipal wastewater treatment plant (WWTP), this research investigated and proposed feasible solutions, control system configurations and optimal operating conditions for the dairy wastewater processing. The steady state study on adding different daily amounts of dairy wastewater in the WWTP water line revealed the most efficient amount to be treated by finding a minimum of the total nitrogen concentration in the water effluent. The dynamic investigations on adding different daily amounts of diary wastewater demonstrated the incentives of the proposed cascade control system configurations, based on the ammonia or nitrates concentration control in the aerated reactors, associated to nitrates and nitrites concentration control in the anoxic reactor. The best periods of time and duration for scheduling the dairy wastewater processing were searched and found. Preliminary results showed the incentives of the additional dairy wastewater distribution during 2 h, at the highest influent concentration moments. Further investigations, relying on the genetic algorithm optimization method revealed that better daily scheduling of the dairy wastewater addition may be obtained. Compared to normal operation, the optimal scheduling program of the dairy wastewater treatment showed an overall performance index improvement of 13.36%, when the daily 1:52 p.m. moment of time and the duration of about 1 h program, found by optimization, were applied. Results demonstrate the dual incentives of the carbon and nutrients recovery, associated to the energy and effluent quality benefits on WWTP operation.
A rapid, sensitive, economically and ecologically friendly method based on one-step ultrasound-assisted emulsification microextraction (USAEME) and in situ derivatization followed by gas chromatography-mass spectrometry (GC-MS) for simultaneous determination of low molecular benzotriazoles (LMBTs) and benzotriazole-based ultraviolet filters (BUVs) was developed. The optimized method allow quantification of benzotriazole (BT), 4-methylbenzotriazole (4MBT), 5-methylbenzotriazole (5MBT); 5-chlorobenzotriazole (5ClBT), 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzortriazole (UV326) and 2-(2′-hydroxy-5′-(1,1,3,3-tetramethylbutyl)phenyl)benzotriazole (UV329) in municipal and industrial (dairy) wastewater. The method was validated using real influent and effluent wastewater and samples at various stages of the purification process. Obtained relative recoveries were between 77 and 137%, limits of detection (LoDs) from 0.001 to 0.035 µg/L, the repeatability expressed by the coefficient of variation (CV) did not exceed 12%. The use of the method for the determination of the tested compounds in municipal and industrial wastewater showed their presence in most of the tested samples, in concentrations from LoD to 6.11 µg/L. The conducted studies of samples from municipal wastewater treatment plant (WWTP) located in north-eastern Poland showed that the effectiveness of benzotriazole removal by this plant is from 29 to 84%. The load of tested compounds released into the environment by this facility ranges from 2 to 269 mg/day/1000 inhabitants.
Measurements for determining the effect of chemically enhanced primary treatment (CEPT) on the efficiency of pollutant removal from wastewater were carried out using conventional inorganic coagulants PIX113 with polymer A110 (Kemipol, Police, Poland) and unconventional cationic organic coagulants Cofloc (Attana, Coalville, UK) C29510 (Kemipol, Police, Poland) and Sedifloc 575 (3F Chimica, Sandrigo, Italy). The average removal efficiency in the 2-hour sedimentation process was 46%, 34%, 8%, 12% for the total suspended solids, organic matter (COD), total nitrogen, and total phosphorus, respectively. The use of organic coagulants contributed to 14–81% increase of pollutant removal efficiency. Substantial discrepancies in biological nutrient removal processes were not discovered in two-phase (anaerobic-anoxic) experiments without and with the addition of the organic coagulants. The increase in organic matter removal efficiency as a result of the CEPT process may contribute to a 65–80% increase in biogas production. The conducted research confirms the possibility of using organic coagulants in the primary precipitation process in wastewater treatment plants (WWTPs) in accordance with the principles of maximum energy recovery, thereby promoting renewable energy sources. Additionally, organic coagulants, as opposed to inorganic ones, do not cause a significant increase of chloride and sulfate ion concentrations, which facilitates the use of treated wastewater in the water reuse systems, such as irrigation of agricultural crops.
In this work, the performance of a sequencing batch reactor (SBR) was studied for treating sanitary wastewater of Yazd power plant, Iran. For this purpose, at the first, a pilot system was designed, installed, and started up. Then the effects of retention time, pH, temperature, influent chemical oxygen demand (COD) concentration, and air flow rate were investigated on the effluent concentration of COD. In SBR reactor used in the Yazd power plant, the microalga was not used for the wastewater treatment. In this case, the COD effluent output was, at the best conditions, approximately 92 mg/L. In the studied SBR system, we used the Chlorella vulgaris microalgae and microorganisms, simultaneously. In this case, the COD level reached 34 mg/L. An artificial neural network (ANN) was developed by applying Levenberg‐Marquardt training algorithm to predict the effluent concentration of COD. The optimum conditions were obtained at pH = 8, temperature of 30°C, influent COD concentration of 600 mg/L, and air flow rate of 50 L/min. ANN predicted results were in good agreement with the experimental data with a validation coefficient of determination (R²) and validation mean square error of 0.962 and 0.0015, respectively.
Paper presents artificial neural network models (ANN) approximating concentration of selected nitrogen forms in wastewater after sequence batch reactor operating with aerobic granular activated sludge (GSBR) in the anaerobic and aerobic phases. Aim of the study was to determine parameters conditioning effectiveness of selected nitrogen forms removal in GSBR reactor process phases. Models of artificial neural networks were developed separately for N-NH4, N-NO3 and total nitrogen concentration in particular process phases of GSBR reactor. In total, 6 ANN models were presented in this paper. ANN models were made as multilayer perceptron (MLP), which were learned using the Broyden-Fletcher-Goldfarb-Shanno algorithm. Developed ANN models indicated variables the most influencing of particular nitrogen forms in aerobic and anaerobic phase of GSBR reactor. Concentration of estimated nitrogen form at the beginning of anaerobic or aerobic phase, depending on ANN model, in all ANN models influenced approximated value. Obtained determination coefficients varied from 0.996 to 0.999 and were depending on estimated nitrogen form and GSBR process phase. Hence, developed ANN models can be used in further studies on modeling of nitrogen forms in anaerobic and aerobic phase of GSBR reactors.
There has been increased interest towards maximizing wastewater energy recovery by enhancing the carbon captured through the primary treatment process such as chemically enhanced primary treatment (CEPT). This research was conducted to optimize the CEPT performance in terms of redirection of carbon and nutrients in both bench- and full-scale operations. In order to improve the CEPT process, the performance of ferric chloride and seven types of polymers were evaluated through jar testing. The optimal coagulant (15 mg/L ferric chloride) and flocculant (0.5 mg/L poly aluminum chloride (PACl)) combination achieved total COD, soluble COD, total suspended solids (TSS), and total phosphorus (TP) removal efficiencies of 76, 58, 89, and 84, respectively, in a full-scale primary clarifier operation. In doing so the organic matter and phosphorus were concentrated in CEPT sludge, making them available for recovery. Furthermore, the relationship between influent characteristics and removal rates under varying operating conditions was investigated. It was found that soluble COD removal appeared to be season-dependent, and TSS removals were independent of influent TSS concentrations in all scenarios. The removal of tCOD, sCOD, and TP had a positive relationship with their corresponding concentrations when the polymer Alcomer® 120L was used, whereas no correlation between removal and concentration was observed with PACl.
Chemicals addition at the mechanical part of wastewater treatment plant can improve overall treatment efficiency and help in solving some plant’s operational problems. Application of such process in the primary clarifiers, named as Chemically Assisted Primary Sedimentation, can also be a huge step towards energy balance improvement for the whole plant. Use of relatively cheap coagulants, such as ferric or alum salts can be an easy way to increase treatment efficiency significantly, as coagulation and flocculation intensifies followed by chemical precipitation. Additional removal of soluble pollutants and suspended solids increases their load in the primary sludge, avoiding their potential removal in the biological part of the plant. Additional organic matter in the primary sludge allows to produce more gas in the anaerobic digestion process and thus increase energy production by the CHP units. Efficiency of different coagulation agents (PIX 109 and PAX XL3) supported by polymer addition was investigated using real municipal wastewater collected from a large Polish wastewater treatment plant (over 500 000 p.e.) in a series of lab-scale tests. Proper selection of coagulant and potential polymer dosage has a serious impact on the overall costs of this additional treatment and energy balance. Based on obtained results, economic analysis was performed for the same plant to evaluate potential gains and losses of implementing such practice.
Municipal WWTP often receive industrial wastewater including bakery sewage. The effluent of bakery industry has a high biological oxygen demand (BOD). In addition to high BOD this wastewater contains high chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN) and dark color. The effect of bakery wastewater contribution on COD fraction changes in municipal sewage is presented in this paper. The study was conducted in July 2016 in WWTP located in Lipsk, East-North Poland. The sewage receiver is the Biebrza River. Volume contribution of bakery wastewater is 10%. Analytical results were used to compute the percentage value contribution of individual COD fractions in wastewater. During the study the following fractions were identified: SS – COD of readily-biodegradable dissolved organic matter, SI – COD of non-biodegradable dissolved organic matter, XS – COD of slowly-biodegradable non-soluble organic matter, XI – COD of non-biodegradable non-soluble organic matter. The method used for COD fraction determination in wastewater was developed based on ATV 131P guidelines (ATV-DVWK-A131P).
The aim of the study was to determine the effect of bakery wastewater contribution on COD fraction changes during technical scale biological wastewater treatment with an activated-sludge process. The percentage contribution of individual COD fractions in wastewater were compared with shares in wastewater from other food industries (dairy, olive mill, tomato, sugar beet, potato processing, winery).
In raw wastewater XS fraction was dominant 44.2%. SS fraction was 38.8%. In raw wastewater fractions SI, XI ranged from 2.3 to 14.8%. In the effluent the SS fraction wasn’t noted, which is indicative of microorganisms consumption. WWTP effluents were dominated (43.4%) by slowly-biodegradable non-soluble organic matter (XS). Non-biodegradable dissolved organic matter (SI fraction) had a high share of 42.3%.
Wastewater treatment is a process which aims to reduce the concentration of pollutants in wastewater to the level allowed by current regulations. This is to protect the receivers which typically are rivers, streams, lakes. Examination of the quality of treated wastewater allows for quick elimination of possible negative effects, and the study of water receiver prevents from excessive contamination. The paper presents the results of selected physical and chemical parameters of treated wastewater from the largest on the region in north-eastern Poland city of Bialystok municipal wastewater treatment and Biała River, the receiver. The samples for research were taken 3–4 a month in 2015 from two points: before and after discharge. The impact of the wastewater treatment plant on the quality of the receiver waters was studied by using non-parametric Wilcoxon test. This test determined whether the analyzed indicators varied significantly depending on different sampling points of the river, above and below place of discharge of treated wastewater. These results prove that the treated wastewater does not affect the water quality in the Biała River.
The paper presents the results of studies concerning the designation of COD fraction in raw wastewater. The research was conducted in four municipal mechanical-biological sewage treatment plants and one industrial sewage treatment plant. The following fractions of COD were determined: non-biodegradable (inert) soluble SI, biodegradable soluble fraction SS, particulate slowly degradable XS and particulate non-biodegradable XI. The methodology for determining the COD fraction was based on the ATV-A131 guidelines and Łomotowski-Szpindor methodology. The real concentration of fractions in raw wastewater and the percentage of each fraction in total COD are different from data reported in the literature.
The paper presents results of studies conducted in terms of the quality of grey- water depending on the selected household chemicals in solid and liquid form. The following physico-chemical parameters were taken into account: pH, COD, BOD5, color, total phosphorus, total nitrogen, nitrates, nitrites, ammonia, total suspended solids, dry residue, conductivity, decay and turbidity. The analysis of parameters depending on the used household chemicals and changes over time were presented.
CAPS is the acronym for chemically assisted primary sedimentation, which consists of adding chemicals to raw urban wastewater to increase the efficacy of coagulation, flocculation and sedimentation. The principal benefits of CAPS are: upgrading of urban wastewater treatment plants; increasing efficacy of primary sedimentation; and the major production of energy from the anaerobic digestion of primary sludge. Metal coagulants are usually used because they are both effective and cheap, but they can cause damage to the biological processes of anaerobic digestion. Generally, biodegradable compounds do not have these drawbacks, but they are comparatively more expensive. Both metal coagulants and biodegradable compounds have preferential and penalizing properties in terms of CAPS application. The problem can be solved by means of a multi-criteria analysis. For this purpose, a series of tests was performed in order to compare the efficacy of several organic and mixed-organic polymers with that of polyaluminium chloride (PACl) under specific conditions. The multi-criteria analysis was carried out coupling the simple additive weighting method with the paired comparison technique as a tool to evaluate the criteria priorities. Five criteria with the following priorities were used: chemical oxygen demand (COD) removal > turbidity, SV60 > coagulant dose, and coagulant cost. The PACl was the best alternative in 70% of the cases. The CAPS process using PACl made it possible to obtain an average COD removal of 68% compared with 38% obtained, on average, with natural sedimentation and 61% obtained, on average, with the best PACl alternatives (cationic polyacrylamide, natural cationic polymer, dicyandiamide resin).
A three-pronged coordinated research effort was undertaken by cooperating utilities at three different experimental scales investigating bioaugmentation, enrichment and performance of anammox organisms in mainstream treatment. Two major technological components were applied: density-based sludge wasting by a selective cyclone to retain anammox granules and intermittent aeration to repress nitrite oxidizers. This paper evaluates process conditions and operation modes to direct more nitrogen to the resource-saving metabolic route of deammonification.
Normalizations by TSS or P-PO43- initial concentrations are consistent as they are correlated to the Jar-test performances. Jar-tests results are independent of the wastewater quality variations in terms of TSS and P-PO43- and independent of the WWTP origin of the water. A notable variability in the TSS results indicates that the pollutant's initial load has to be taken into account even with normalizations. This variability is lower with normalization by P-PO43-, indicating that this is the best indicator to consider. It is possible to determine that the optimal cation dosage is 60 mol Fe3+ / kg P-PO43- as it guarantees a residual concentration of 0.7-1.0 mgP/L and a good removal of TSS. Then, six commercially available cationic coagulants were compared, demonstrating a comparable effect at a comparable normalized molar dose, whatever the coagulant on both TSS and P-PO43-, as well as on soluble carbon and nitrogen. The differences observed between these types of coagulants in the literature are then probably due to methodological issues. Settling velocity distribution charts were also very similar for the different coagulants. This confirms that the source of cation and the type of cation have no significant effect on physico-chemical settling performances.
Engineered nanoparticles (ENPs) present in natural water systems and wastewater treatment plants, due to their wide use in industrial products and consumer goods, represent a hazard to human health, especially if occur in surface waters used for human consumption. Different nanoparticles may co-exist in the natural waters and until now no works have been developed on the impact of the co-existing nanoparticles on water treatment processes. Thus, this work evaluates the removal of different co-existing metal-based ENPs (TiO2, Ag and CuO) from natural surface waters applying the most used water treatment process, coagulation/flocculation/sedimentation (C/F/S). Results showed that C/F/S is effective in the removal of the co-existing ENPs from the studied hydrophilic natural waters (low/medium turbidity and moderate/moderate-high natural organic matter content) with efficiencies above 93% for TiO2, Ag and CuO nanoparticles. The formation of destabilised nanoparticle-organic matter aggregates in C/F promoted their precipitation. For the lowest turbidity and organic content water, Ti presented the lowest concentration, followed by Ag and Cu, because of titanium properties. For the highest turbidity and organic content water, the residual Cu concentration was the lowest and Ag the highest, due to the natural water characteristics. Water characteristics played an important role on the coagulant demand and removal of ENPs mixture by C/F/S. Results also demonstrated that ENPs mixture did not hampered the treated water quality for turbidity and natural organic matter. For the lowest turbidity and natural organic matter water, ENPs appear to contribute to a higher removal of these parameters.
Discharge of treated municipal wastewater containing arsenic (As) may cause adverse effects on the environment and drinking water sources. Arsenic concentrations were measured throughout the treatment systems at two municipal wastewater plants in New Jersey, USA. The efficiency of As removal by ferric chloride and alum coagulants were evaluated. Besides, the effects of suspended solids in the mixed liquor, pH, and orthophosphate (PO4³⁻) on As removal were investigated. The total recoverable As (TAs) concentrations in the influent and effluent of Plant A were in the ranges of 2.00–3.00 and 1.50–2.30 μg/L, respectively. The results indicated that <30% of the As was removed by the conventional biological wastewater treatment processes. The influent and effluent TAs concentrations at Plant B was below 1.00 μg/L. The bench-scale coagulation results demonstrated for the first time that the coagulation treatment could not effectively remove As from the municipal wastewater to <2.00 μg/L. Very high doses of the coagulants (8 and 40 mg/L of Fe(III) or Al(III)) were required to reduce the TAs from 2.84 and 8.61 μg/L in the primary clarifier effluent and arsenate-spiked effluent samples to <2.00 μg/L, respectively, which could be attributed to the high concentrations of PO4³⁻ and dissolved organic matters (DOM) in the wastewater. The protein DOM in wastewater may negatively impact removal efficiencies more than the DOM in natural water, which mainly consists of humic substances. Furthermore, an artificial neural network was constructed to determine the relative importance of different parameters for As removal. Under the experimental conditions, the importance followed the order: coagulant dose>dissolved PO4³⁻ > initial As concentration > pH. The findings of this study will help develop effective treatment processes to remove As from municipal wastewater.
“Clean water and sanitation” is one of the 17 sustainable development goals recommended by the United Nations. To improve water quality, China had experienced a dramatic improvement in municipal wastewater treatment during 2006–2016; yet the effects on pollutant reductions have not been fully discussed. This study analyzed pollutant reductions and operating costs of municipal wastewater treatment according to an investigation including 1822 active wastewater treatment plants in operation in China. The results showed that, in 2016, a total of 505 Gg of total nitrogen, 140 Gg of ammonia, 29 Gg of total phosphorus, 1296 Gg of chemical oxygen demand and 357 Gg of five-day biochemical oxygen demand were discharged after treatment. The highest pollutant removal efficiency from municipal wastewater was observed in five-day biochemical oxygen demand, with an efficiency of 91.2 ± 6.7% (average and standard deviation), while the lowest removal efficiency was observed in total nitrogen, only with an efficiency of 65.5 ± 13.9%. The higher total phosphorus removal efficiency (80.8 ± 11.8%) by wastewater treatment could increase the ratio of total nitrogen to total phosphorus by about twice in the effluent. Water managers should focus on the potential impacts of effluents to nutrient dynamics and ecology in receiving waters. Modern perspectives on nutrient limitation in aquatic ecosystems will require more N removal from municipal wastewater to achieve the desired water quality outcomes, such as by refining operation of existing facilities, developing efficient N-removal technology and introducing standards for nutrient ratio target in the effluent discharge.
The main objective of wastewater treatment is to remove carbon and other nutrients from municipal and industrial effluents in order to protect the environment and human health. Typical wastewater treatment is usually achieved by a combination of physical, chemical and biological methods. In this work, municipal wastewater was depurated using chemically enhanced primary treatment (CEPT) in combination with a pilot-scale trickling filter. Lab scale experiments (Jar-tests) were carried out in order to determine the optimum dosage of chemicals. Selection criteria were the organic load removal efficiency and the low operational cost. Coagulation-flocculation process was conducted through polyaluminium chloride (PAC) and the cationic polyelectrolyte (Zetag 8180) addition. By combining CEPT and trickling filter, tCOD (total Chemical Oxygen Demand), sCOD (soluble Chemical Oxygen Demand), BOD5 (5-day Biochemical Oxygen Demand), NH4⁺-N, TSS (Total Suspended Solids), VSS (Volatile Suspended Solids) and PO4³⁻-P removal efficiencies were estimated to be 89, 82, 93, 60, 96, 96 and 78%, respectively. It is concluded that biological filtration contributed significantly in nutrients removal processes. Moreover, the obtained effluent was low in carbon and rich in nitrogen, which can be applied for restricted irrigation after disinfection, complying with the discharge limits set in the Greek Joint Ministerial Decree 145116/2011.
A comparative study of the efficiency of different coagulants in the textile wastewater treatment was carried out. The utilization of natural coagulants instead of the synthetic ones has demonstrated significant advantages since it provides a low cost and environmentally friendly technology for removing dyes. This study aimed at evaluating the performance of different coagulants in the removal of the apparent colour, turbidity, absorbance, and COD of textile wastewater samples from an industrial laundry. Two organic coagulants (Moringa oleifera Lam seeds extracted in saline solutions of NaCl and KCl 1 mol L⁻¹) and an inorganic coagulant (aluminium sulphate) were used. Initially, the influence of the pH was evaluated for each coagulant. Then, a factorial design was applied in order to determine the coagulant concentration and the sedimentation time needed for the textile wastewater treatment. All the parameters obtained their best results with acidic pH values for the studied coagulants. The organic coagulants presented the best results, in general, reaching removals of 82.2% for the apparent colour, 83.05% for COD, 78.4% for RP-HE7B, and 89.7% for OP-HER using the Moringa coagulant extracted in KCl. This study demonstrated the applicability of the Moringa oleifera Lam seeds to the textile wastewater treatment.
In the present study, simultaneous management of water and wastewater was examined using ant and artificial neural network algorithms. Ant algorithm is one of the most meta-heuristic algorithms to solve optimization problems. The data were collected in a monthly time series from the Regional Water Organization of Khorasan Razavi during 1998–2016. Water flow data were initially estimated in the study. In this regard, different structures of the back propagation network (1, 2, 3, 4 and 5 nodes in the hidden layer) were designed by using logistic activation function in order to evaluate the efficiency of ANN model and its comparison with the ARIMA method in predicting the time series of the flows for the time horizons of next 3, 6, 9 and 12 month. The output data of each network were finally compared with actual data to evaluate the efficiency of the model and its comparison with ARIMA model using the evaluation criteria of models. Water resources were, then, allocated to drinking, agricultural and industrial sectors using the ant algorithm. According to the results of the total consumption of drinking water for the industrial sector, the southeast and northwest of Mashhad have the greatest amount of water. In other words, the northeastern and southwestern parts of Mashhad have the least amount of water for the industrial sector. And so, there must be a higher priority to water scarcity in these two regions than the other areas.
In the present study, chemical coagulation with alum and polyaluminium chloride (PACl) was utilized for greywater treatment. More than 140 jar tests on greywater with varying characteristics were conducted in order to determine the optimum coagulant dosage and treated greywater characteristics. The average removal efficiencies of turbidity, chemical oxygen demand (COD) and total suspended solids were obtained as 91, 73 and 83% using alum and 93, 74 and 89% using PACl, respectively. For similar initial turbidity levels, optimum PACl dosages required were significantly less compared to optimum alum dosages. Further, PACl produced treated greywater with lower levels of turbidity compared to alum. Results of the coagulation tests were used to design artificial neural network (ANN) models for the prediction of the optimum coagulant dosage and treated greywater quality parameters. ANN models with initial turbidity, pH, conductivity and alkalinity as the input parameters could predict the optimum coagulant dose and treated greywater quality. The performance of the models was found to be good, with correlation coefficient values greater than 0.80. Empirical formulas for the prediction of alum and PACl dosages were also derived using the algorithm weights and bias values from the networks eliminating the need for running the ANN software.
The annual global production of milk is approximately 630,000 million litres and the volume of generated dairy wastewater accounts for 3.2 m3·m-3 product. Dairy wastewater is characterized by a high load of chemical oxygen demand (COD). In many wastewater plants dairy wastewater and municipal wastewater are co-treated. The effect of dairy wastewater contribution on COD fraction changes in municipal sewage which has been treated with a sequencing batch reactor (SBR) in three wastewater treatment plants in north-east Poland is presented. In these plants the real contribution of dairy wastewater was 10, 13 and 17%. In raw wastewater, SS fraction (readily biodegradable dissolved organic matter) was dominant and ranged from 38.3 to 62.6%. In the effluent, SS fraction was not noted, which is indicative of consumption by microorganisms. The presence of dairy wastewater in municipal sewage does not cause changes in the content of the XI fraction (insoluble fractions of non-biodegradable organic matter). SBR effluents were dominated by non-biodegradable dissolved organic matter SI, which from 57.7 to 61.7%. In raw wastewater SI ranged from 1.0 to 4.6%. Xs fraction (slowly biodegradable non-soluble organic matter) in raw wastewater ranged from 24.6 to 45.5% while in treated wastewater it ranged from 28.6 to 30.8%. In the control object (fourth wastewater plant) which does not process dairy wastewater, the SS, SI, Xs and XI fraction in inflow was 28.7, 2.4, 51.7 and 17.2% respectively. In the effluent the SS, SI, Xs and XI fraction was below 0.1, 33.6, 50.0 and 16.4% respectively.
The processes necessary for transformation of cassava into starch generate several residues, among them cassava wastewater (manipueira) that has high pollutant load. For the effluent treatment system it is essential to remove sedimented suspended solids, which can be performed by the coagulation/flocculation/sedimentation process (C/F/S), requiring a comparative study between coagulants for the successful selection of the coagulant and its dosage. Therefore, the aim of this work was to investigate the efficiency of different coagulants in color and turbidity removal of starch industry effluent. In this way, jar-test experiments were conducted. Four natural commercial coagulants (Acquapol WW, Acquapol S5T, Tanfloc SL, Tanfloc SG) and a chemical coagulant (Al2SO4) were tested at concentrations of 160, 320, 480, 640 and 800 mg L⁻¹, setting the fast mixing stage for 2 min at 120 rpm and the slow mixing stage for 15 min at 20 rpm, at natural pH of the effluent. Among the studied coagulants, natural commercial coagulants presented greater efficiency of color and turbidity removal when compared to chemical coagulant, besides having the advantage of being non-toxic and from renewable source. All coagulants had a minimum sedimentation time of 15 min. The best natural coagulant (Acquapol S5T and Tanfloc SL) concentration determined from statistical analysis (ANOVA, p-value <0.05; Turkey's test, p-value >0.05) was 320 mg L⁻¹, capable in removing color (≥77.5%) and turbidity (≥88.5%) parameters for treatment of the studied effluent. The C/F/S process employing these two selected coagulants proves to be an effective physico-chemical method for primary treatment of this type of effluent, contributing to the improvement in wastewater quality.
The effects of a commercially produced Tannin-based coagulant and flocculant (Tanfloc) in a biofilm process pilot plant treating municipal wastewater were investigated. The investigated flow rates were 10, 14 and 18 L/min for the entire pilot plant, with two additional flows of 22 and 24 L/min were used for flocculation and sedimentation processes only. There was no clear deterioration in flocculation efficiency; even at 24 L/min, where the flocculation time was only 7.5 min. In terms of the clarification process, the enhancement was remarkably good; especially at high flows. Without Tanfloc, the removal efficiencies in the clarifier were less than 20%, 40%, 22% and 8% for turbidity, total suspended solids, biochemical oxygen demand and total phosphate, respectively. Meanwhile, when Tanfloc was used, they achieved 75%, 61%, 60% and 16% for the same respective pollutants. A significant rise in dissolved oxygen level in the aeration tank was observed when Tanfloc was applied (promising saving of energy during aeration). For instance, a dissolved oxygen level of 3 mg/L measured in experiments without Tanfloc, witnessed a climb to 6 mg/L when Tanfloc was used. In addition, volatile suspended solids concentration in the aeration tank decreased when Tanfloc was used (promising less production of sludge). Other measurements of total suspended solids (mg/L), chemical oxygen demand (mg/L) and biochemical oxygen demand (mg/L) in the experiments without Tanfloc were in the range (12–36), (60–104) and (24–50), respectively. Remarkably Tanfloc was able to reduce these measurements to low levels of (9–26), (28–68) and (7–24). In conclusion, the results suggest Tanfloc as promising agent to enhance the performance of clarification in a biological treatment unit. In light of this enhancement, Tanfloc could be used to upgrade existing treatment plants or design compact treatment units.
It is becoming increasingly important to control the discharge of industrial wastewater from industrial parks in order to reduce water pollution. In this study, a comprehensive investigation of water treatment at industrial parks in two large basins in China was carried out, involving comparative and correlation analysis of wastewater quality, pollutant removal, sludge production and cost. In both basins, the average influent chemical oxygen demand, ammonia, and total nitrogen at the centralized wastewater treatment plants in chemical parks were higher than those in comprehensive parks. Anaerobic-anoxic-oxic and anoxic-oxic were the most widely used treatment processes at both comprehensive and chemical parks in the two basins-similar to municipal wastewater treatment plants in China. The operating costs of centralized wastewater treatment plants in the comprehensive and chemical parks comprised the following components: electricity > labor > chemical costs. Reductions in chemical oxygen demand, ammonia and total nitrogen and total phosphorus in the centralized wastewater treatment plants in the parks led to an average reduction of 28% in total pollutants in municipal and industrial wastewater in the two basins. These results could have supports for the design and optimization of wastewater treatment processes, as well as for evaluation of how centralized wastewater treatment plants can help to control water pollution.
The technical performance, economic cost and environmental impact of six full-scale tertiary coagulation/filtration processes located in Kunming, China were evaluated. All tertiary treatment processes removed total phosphorus (TP) and total suspended solids (TSS) efficiently, with the removal percentages of 55.0%–80.0% and 50.0%–74.0%, respectively. Polyaluminium chloride (PAC) consumption for TP and TSS removal in the six tertiary treatment processes were quite different, with chemical dosages of 7.9–38.5 g PAC/g TP removed and 0.3–1.7 g PAC/g TSS removed, respectively. The multiple linear regression analysis showed that the PAC dosage closed to the optimal value benefited TP and TSS removal, and this also reduced the economic cost. For environmental impacts, the main source of greenhouse gas was electricity consumption and the coagulation/filtration process had positive effect on reducing eutrophication. The comprehensive assessment including technical, economic and environmental aspects was characterized by the composite cost index. The composite cost index showed that the tertiary treatment process of micro-flocculation with D type/cloth media filtration achieved the best comprehensive performance, while D type filter had great potential for energy saving and chemical reduction.
The paper presents a model-based evaluation of technological upgrades on the energy and cost balance in a large biological nutrient removal (BNR) wastewater treatment plant (WWTP) in the city of Slupsk (northern Poland). The proposed upgrades include chemically enhanced primary sludge removal and reduction of the nitrogen load in the deammonification process employed for reject water treatment. Simulations enabled to estimate the increased biogas generation and decreased energy consumption for aeration. The proposed upgrades may lead the studied WWTP from the energy deficit to energy neutrality and positive cost balance, while still maintaining the required effluent standards for nitrogen. The operating cost balance depends on the type of applied coagulants/flocculants and specific costs of electric energy. The choice of the coagulant/flocculent was found as the main factor determining a positive cost balance.
The energy balance of a municipal wastewater treatment (WWT) system was evaluated considering the influence of excess biological sludge anaerobic biodegradability (BDAn) and of biogas utilisation as either fuel for co-generation of heat and power (CHP) or for vehicle transport. Sludge thermal pre-treatment prior to anaerobic digestion and high-rate carbon removal were considered as modifications of a reference municipal WWT system to impact the sludge BDAn. Both thermal pre-treatment and a high-rate process with a short sludge retention time (SRT = 1-3d) led to ∼30% higher sludge BDAn than that of untreated sludge from a low-rate WWT system with long SRT ( > 8d), which enhanced methane yields and energy production correspondingly. An efficient separation (40% of CODin) of primary solids promoted biogas production by capturing a significant part of the incoming COD, and lowered aeration energy demands for carbon oxidation due to lower loads of particulate organics into the biological treatment. Thermal pre-treatment can most effectively increase the biodegradability of sludge originating from a low-rate WWT system with a long SRT. Sludge solubilization alone as an indicator of increase biodegradability by a pre-treatment is inadequate for sludge types with inherently high biodegradability. A WWT system with primary separation, sludge pre-treatment, and CHP from biogas can be a net electricity producer and self-sufficient in thermal energy, provided the thermal energy from CHP is available for the pre-treatment. With other types of energy carriers as inputs and outputs, the WWT performance also needs evaluation with respect to the energy economic and environmental value.
Chemically Assisted Primary Sedimentation (CAPS) consists of adding chemicals in order to increase the coagulation, flocculation and sedimentation of raw urban wastewater. The CAPS process can be developed in order to increase the efficacy of primary sedimentation as well as avoid any interference with biological treatment processes. The application of CAPS is particularly suitable as a technique for the upgrading of urban wastewater treatment plants (UWWTPs). In fact, CAPS does not require any further significant structural intervention (so saving investment costs and territory portions). The aim of this contribution is to emphasise the role of CAPS as a green chemistry option available in a UWWTP. In particular, a specific aim of the chapter is to focus the attention on the energetic importance of CAPS due to its capacity to increase the production of the primary sludge and consequently the energy production with an anaerobic digestion treating separately primary and secondary sludge. The energetic convenience and “green” propensity of the application of CAPS is discussed by means of the presentation of a paradigmatic case study containing economic evaluations, as well.
The composition of wastewater from tourist areas is discussed. Since such a significant part of the contaminants in wastewater is associated with particles, a good particle removal should be the first step in the treatment of wastewater. In coastal areas it is recommended that coagulation with lime should be used. Special attention is drawn to the lime/seawater process where 2-5 vol-% of seawater is added to the influent resulting in several process improvements. For low-cost treatment the use of the lime/seawater process in a pond system is discussed.
Chemically enhanced primary treatment (CEPT) is a wastewater treatment method that serves as an attractive alternative to the conventional primary treatment, and it can also be used as an efficient preliminary step of the biological secondary treatment processes. CEPT adopts coagulation and flocculation and it accomplishes remarkable increases in the removal of common pollutants from the influent. The coagulants used in the present study were alum, sea-salt as a cheap coagulant, and homogenous mixtures of sea-salt (as a coagulant aid) and alum with different doses.These alternatives were tested in the direct precipitation of wastewater. The analytical hierarchy process was applied for the evaluation of different alternatives of coagulants according to four main criteria (i.e. removal efficiencies, sludge volume after 30 min, coagulant cost, and pH variation). In addition, the removal efficiencies were divided into five subcriteria, including COD, BOD5, TSS, T–P, and T–N removals. The obtained results revealed that the removal efficiencies reached up to 87% of COD, 93% of BOD5, 94% of TSS, 96% of T–P, and 20% of T–N greatly reducing the settling time in the primary treatment to about 30 min rather than 2 h in the conventional primary sedimentation. This creates a simple procedure for the optimization of chemical precipitation for wastewater treatment.
Chemically Enhanced Primary Treatment (CEPT) or Chemically Assisted Primary Sedimentation Process (CAPS) involves the use of chemical coagulants to enhance the coagulation or flocculation of wastewater particles. The effect of a metal salt, ferric chloride (FeCl3) and an anionic polymer on the removal of suspended solids (SS) of wastewater collected from two sewage treatment plants was studied by jar test experiments. The results showed that the optimum dosage for the removal of 60% of SS was 30 ppm of FeCl3 with 0.5 ppm polymer. A larger scale test further revealed that the addition of 30 ppm of FeCl3 and 0.5 ppm. polymer could provide a reduction of SS, total nitrogen (N) and total phosphorous (P) higher than 80%, 70% and 40%, respectively. The experimental results confirmed that CAPS can be used as an alternative for the treatment of sewage to traditional biological processes.
In seeking greater sustainability in water resources management, wastewater is now being considered more as a resource than as a waste-a resource for water, for plant nutrients, and for energy. Energy, the primary focus of this article, can be obtained from wastewater's organic as well as from its thermal content. Also, using wastewater's nitrogen and P nutrients for plant fertilization, rather than wasting them, helps offset the high energy cost of producing synthetic fertilizers. Microbial fuel cells offer potential for direct biological conversion of wastewater's organic materials into electricity, although significant improvements are needed for this process to be competitive with anaerobic biological conversion of wastewater organics into biogas, a renewable fuel used in electricity generation. Newer membrane processes coupled with complete anaerobic treatment of wastewater offer the potential for wastewater treatment to become a net generator of energy, rather than the large energy consumer that it is today.
When a new wastewater treatment plant is being designed by computer simulation, detailed data about organic fractions of influent wastewater (measured as chemical oxygen demand) are usually not available, but knowledge of the typical ranges of these fractions is indispensable. The influent chemical oxygen demand fractions can substantially influence the results of simulation-based design such as reactor volumes, solids residence time, effluent quality, oxygen demand, sludge production, etc. This article attempts to give an overview of wastewater organic fractions as modeling parameters and presents new chemical oxygen demand fractionation results from Hungary. According to the data from literature, the ratio of chemical oxygen demand components in raw wastewater is very different and the average composition is as follows: Inert particulate = 17.1 %, slowly biodegradable = 57.9 %, inert soluble = 7.8 % and readily biodegradable = 17.5 %. The Hungarian wastewater samples were analyzed according to STOWA (Dutch foundation for applied water research) protocol and the obtained results were not much different from those of literature ( inert particulate = 23.7 %, slowly biodegradable = 49.8 %, inert soluble = 4.6 % and readily biodegradable = 21.9 %), but some typical characteristics were observed.
The microbiology and the feasibility of a new, single-stage, reactor for completely autotrophic ammonia removal were investigated. The reactor was started anoxically after inoculation with biomass from a reactor performing anaerobic ammonia oxidation (Anammox). Subsequently, oxygen was supplied to the reactor and a nitrifying population developed. Oxygen was kept as the limiting factor. The development of a nitrifying population was monitored by Fluorescence In Situ Hybridization and off-line activity measurements. These methods also showed that during steady state, anaerobic ammonium-oxidizing bacteria remained present and active. In the reactor, no aerobic nitrite-oxidizers were detected. The denitrifying potential of the biomass was below the detection limit. Ammonia was mainly converted to N2 (85%) and the remainder (15%) was recovered as NO3-. N2O production was negligible (less than 0.1%). Addition of an external carbon source was not needed to realize the autotrophic denitrification to N2.
In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant significantly reduces the nitrogen load of the activated sludge system. Two biological applications are considered for nitrogen elimination: (i) classical autotrophic nitrification/heterotrophic denitrification and (ii) partial nitritation/autotrophic anaerobic ammonium oxidation (anammox). With both applications 85-90% nitrogen removal can be achieved, but there are considerable differences in terms of sustainability and costs. The final gaseous products for heterotrophic denitrification are generally not measured and are assumed to be nitrogen gas (N2). However, significant nitrous oxide (N2O) production can occur at elevated nitrite concentrations in the reactor. Denitrification via nitrite instead of nitrate has been promoted in recent years in order to reduce the oxygen and the organic carbon requirements. Obviously this "achievement" turns out to be rather disadvantageous from an overall environmental point of view. On the other hand no unfavorable intermediates are emitted during anaerobic ammonium oxidation. A cost estimate for both applications demonstrates that partial nitritation/anammox is also more economical than classical nitrification/denitrification. Therefore autotrophic nitrogen elimination should be used in future to treat ammonium-rich sludge liquors.
Modelling and Simulation of Activated Sludge Process in the Context of Energy Management of Sewage Treatment Plants
- P Balbierz
P. Balbierz, Modelling and Simulation of Activated Sludge Process in the Context of
Energy Management of Sewage Treatment Plants, PhD thesis, University of Science
and Technology, Wrocław, 2016.
- E W Rice
- R B Baird
- A D Eaton
- L S Clesceri
E.W. Rice, R.B. Baird, A.D. Eaton, L.S. Clesceri, Standard Methods for the
Examination of Water and Wastewater, 22nd edition, Ame. Pub. Hea. Ass. (APHA),
Ame. Wat. Wor. Ass. (AWWA), Wat. Envir. Fed. (WEF), 2012.