Article

Cost analysis of large scale membrane treatment systems for potable water treatment

Authors:
  • Istanbul Technical University/Delft University of Technology
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Abstract

Along with the increasing world population, the water sources are faced with considerably serious problems in terms of quantity, quality and all other sector-specific usages. Today, brackish water, surface water, seawater and even wastewater can be treated to supply drinking water. Reverse osmosis, nanofiltration, ultrafiltration and microfiltration are the most widely used membrane processes for the treatment of these water sources. It is necessary to calculate the total cost, including both capital expenses and operation and maintenance expenses such as energy labor, membrane replacement, chemicals and concentrate disposal to determine the most economical design. In this study, the costs of large scale membrane systems for the treatment of brackish, surface and seawater to obtain drinking water were investigated for Turkey. The effects of the Total Dissolved Solids (TDS) concentration, turbidity and salinity values on the treatment costs of brackish water, surface water and seawater were investigated, respectively taking into consideration also the variations in capacity and flux values.

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... Firstly, the cost of chemical cleaning is high, including the chemical and personnel maintenance costs. In a large-scale groundwater RO desalination plant (100,000 m 3 /day), the chemicals cost for cleaning was reported to be around 35% of the total operation costs [167]. Secondly, chemical cleaning may cause membrane degradation, affecting membrane performance and shortening membrane lifetime [163]. ...
Thesis
Decentralised renewable energy-powered desalination technologies provide a promising solution to solve drinking water safety issues in arid rural areas where electricity is not always accessible. Solar energy-powered membrane systems are one of the most mature solar-desalination technologies, suitable for small-scale decentralised brackish water desalination in rural areas due to their economic-technical feasibilities. Batteryless directly coupled photovoltaic-powered nanofiltration/reverse osmosis (PV–NF/RO) shows great advantages over common PV–NF/RO systems with energy storage devices, hence it is targeted in this thesis. However, in such systems, the fluctuation of solar energy causes less water production and unstable system operation. The operating pressure and feed cross-flow will fluctuate and drop to low levels even to zero. When the operating pressure is below the osmotic pressure of feedwater, a direct osmotic backwash (OB) process occurs spontaneously. This spontaneous backwashing process is a potential and preferred self-cleaning method for membrane scaling/fouling in rural areas due to its simplicity. Membrane scaling/fouling is one of the limiting factors in the application of membrane technology. Mineral scalants and organic matter in water can accumulate on the membrane surface or adsorb by the membrane and block the membrane or form a fouling layer, increasing operation and maintenance costs and shortening membrane lifetime. Therefore, the research aims of this thesis are as follows; i) investigate the spontaneous OB mechanism induced by a wide range of solar energy fluctuations with different feedwater salinities (Chapter 5); ii) verify the feasibility and cleaning efficiency of spontaneous OB on membrane mineral scaling and organic fouling control (Chapter 6–8); and iii) explore the impact of spontaneous OB on membrane integrity (Chapter 9). Filtration experiments with OB cleaning were performed using a bench-scale crossflow NF/RO system powered by a solar array simulator (SAS) with different feedwater chemistries (salinity, scalants/foulants concentration, pH, hardness) and two membrane types (BW30 and NF270). The SAS simulates the solar irradiance fluctuation and induces the OB process. OB performance (including OB flux, accumulated backwash volume and effective backwash time) was monitored and quantified by a bi-directional liquid flow sensor. Calcium carbonate and calcium sulphate were selected as model scalants and humic acid with calcium as model organic foulant. Scaled/organic fouled membrane samples with and without osmotic backwash were examined by microscopes to provide direct evidence of OB cleaning efficiency for scaling/fouling. Eleven organic matter types were used to investigate the impact of adhesive interaction between organics and membranes on OB cleaning efficiency. Several key findings are obtained from this thesis; i) solar energy fluctuations cause the variation of system hydrodynamics, operating time and permissible backwash time, influencing the OB performance via affecting the salt concentration polarisation and subsequent driving force; ii) the feasibility of spontaneous OB on scaling and organic fouling control in a bench-scale directly coupled PV–NF/RO system was demonstrated for the first time, which verifies the benefit of direct coupling unstable operation in terms of effective cleaning of spontaneous OB; iii) spontaneous OB is most effective at the initial stage of scaling/fouling, with feedwater at neutral pH, and low salinity and hardness. Once the extent of scaling/fouling or organic matter’s “stickiness” exceeds a certain critical level, the spontaneous OB is ineffective. iv) NF/RO membrane integrity was maintained after 1000 repetitions of spontaneous OB (each 3 min) with sodium chloride solution in the bench-scale system, indicating the spontaneous OB is unlikely to cause membrane integrity loss. These outcomes bring several practical messages/insights for the further development and application of spontaneous OB in directly coupled PV–NF/RO systems; i) the implementation of a small container (volume depending on the membrane area) and a control valve on the permeate side of membrane module to allow sufficient permeate water for spontaneous OB; ii) during sunny days (fewer fluctuations), it is worth considering turning off the pump or reducing the operating pressure for a few minutes to induce the OB cleaning process; iii) the frequency and duration of the OB process (no more than 5 minutes) can be controlled by artificial intelligence (AI, such as machine learning algorithms) based on big data on weather and NF/RO membrane performance/cleanliness during the solar-desalination; and iv) the reliability and effectiveness of spontaneous OB in large-scale directly coupled PV–NF/RO systems can be verified by pilot-scale spiral wound membrane systems.
... The physical and chemical cleaning methods are usually both applied to enhance the cleaning effectiveness [171]. Besides, according to a study on cost analysis of large scale groundwater RO desalination system (100,000 m 3 /day, sand filtration as pretreatment), the chemicals cost for cleaning was reported to be about 35% of the total operation cost [183]. ...
Article
Photovoltaic-powered membrane filtration (PV-membrane) systems are of interest for the provision of clean drinking water in small communities, especially in remote areas. In order to deliver clean water at the lowest cost over the lifetime of the system, a reliable and robust design is paramount. This paper provides a comprehensive review of the operating range and reliability of all components of a small-scale PV-membrane system for brackish water desalination. The failure and degradation modes, as well as lifetime and robustness issues associated with field operation are discussed and best-practice recommendations made. The outcomes of this paper suggest that a small-scale (power rating<1.5 kW) PV-membrane system – based on a helical rotor pump driven by a direct-current brushless motor and powered by silicon photovoltaic modules – may achieve a lifetime of 20 years, while operating with a specific energy consumption of 1.5–3 kWh/m3. Possible methods for mitigating the effects of membrane fouling and damage are also discussed. To maximize membrane lifetime, such systems ought to be operated with a recovery of less than 30% and limit the rate of change of pressure (induced by fluctuations in solar irradiance) to less than 0.7 bar/s. The analysis is useful for identifying the optimal combination of components, system operation and possible reliability improvements. The investigation into component and system failures allows the weakest links to be avoided and enable the optimization of future systems. This review is intended as valuable reference for engineers engaged in the field of renewable-energy-powered membrane filtration technologies.
... This cost was predicted by Elazhar et al. [29] as only 4% and as 15% by Chakrabortty et al. [4]. Ari et al. [34] performed an interesting study to evaluate the costs of desalination in different situations and the comparison between NF and RO resulted in similar water cost for small desalination plants ($0.169/m³ for RO and $0.173/m³ for NF) for treatment of surface water to produce drinking water. ...
Article
Full-text available
The paper reviews the cost of different water supply and water treatment options around the world. The cost of supplying ground water is found to be proportional to the lift. The relationship between cost and volume of water treated by specific treatment options is assessed. Vehicular transportation of water is found to be very costly compared to wastewater treatment and compared to conventional water treatment and supply. Efforts have been made to differentiate the cost of water with respect to its application in various sectors. The capital cost of infrastructure required to extract, treat, supply, and reclaim water is also studied. Finally, the effects of precipitation, geographic aspects, population, financial, regulatory laws, and social attributes of a specific region are considered as they affect the cost of water. Global use of water in agriculture and the costs of agricultural irrigation are studied. Pressurized irrigation systems are costlier compared to flood or surface irrigation systems.
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Economically usable water resources per capita are decreasing due to excessive population increase each year in Turkey. For this reason, new water resources should be found in the near future. The potential water resources are seawater or well water both of which need removal of salinity. The most promising treatment method for salinity is reverse osmosis. While reverse osmosis becomes widespread, the cost of the process will decrease. There is no detailed information about cost of seawater desalination in Turkey. In this study, a cost analysis of seawater desalination in Turkey was performed for reverse osmosis systems. The basic parameters of cost analysis such as capacity, recovery, membrane life, energy, chemical costs and flux were evaluated based on the effects on capital, operating and total production costs.
Article
A new generation of reverse osmosis (RO) membrane has recently been introduced, which is receiving a great deal of interest. This is especially true among application of RO for large-scale municipal desalination systems. This new group of RO membranes operates at very low applied pressure, often in the range of 7–10 bar (100–150 psi). This paper presents information and data on the characteristics and performance of these membranes relative to the traditional brackish RO membranes. Performance and cost comparisons are provided. Also, an existing large-scale facility is reviewed.
Article
In this paper, a predictive model based on the Donnan–Steric–Pore model (DSPM) has been used to develop general criteria for selection of optimum nanofiltration (NF) membranes and to analyse the effect of various nanofiltration membrane characteristics on the cost of NF membrane system. By using an economic assessment model for NF processes, the two most important factors determining the performance of NF membranes which are λ (the ratio of solute radius and membrane pore radius) and ζ (the ratio of membrane charge effective density to bulk concentration) were examined. The optimal conditions for minimum operation cost and optimal operating pressure were also determined. Detailed cost analysis reveals both capital and operating cost were not affected by the variation of ζ. However, decreasing the membrane pore size will increase costs. It was found that up to 30% of the capital and operating costs in recovering sodium sulphate solution can be saved by using looser membrane compared to the tight membrane structure.
Cost a nalysis of seawater desalination with reverse osmosis in T urkey, Desalination Cost components of reverse osmosis system for different water sources
  • D Akgul
  • M Cakmakci
  • N Kayaalp
  • I Koyuncu
D. Akgul, M. Cakmakci, N. Kayaalp and I. Koyuncu, Cost a nalysis of seawater desalination with reverse osmosis in T urkey, Desalination, 220 (2008) 123–131. Fig. 7. Cost components of reverse osmosis system for different water sources.
Cost components of reverse osmosis system for different water sources. Downloaded by
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Fig. 7. Cost components of reverse osmosis system for different water sources. Downloaded by [North West University] at 06:02 21 December 2014
Use of nanofi ltration predictive model in developing criteria for membrane selection and analyzing cost impact
  • N Ali
  • A W Mohammad
  • A L Ahmad
N. Ali, A.W. Mohammad and A.L. Ahmad, Use of nanofi ltration predictive model in developing criteria for membrane selection and analyzing cost impact, Sep. Purif. Tech., 41 (2005) 29-37.