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Sewer Blockage Management: Australian Perspective
Abstract
The functions performed by sanitary sewers can be disrupted by blockages in the pipeline, especially in cities with aging systems and deteriorating pipes. The problem is acute in Australia, where the principal blockage cause is tree root intrusion. This paper presents an overview of the causes of sewer blockages, the scope of the asset management challenge, and the management practices employed by Australian water utilities. These views were developed through reviews of the literature and current management practices elicited in a collaborative research project involving a range of water sector partners and using qualitative techniques such as surveys, interviews, and workshops. This paper highlights that blockages occur because of a range of factors, of which root blockages are the most common in Australia. Issues that confound management of blockages are also described, along with a summary of management strategies. Optimizing the balance between proactive and reactive interventions was found to be a good management strategy to maximize service outcomes.
... The efficiency of the operation and maintenance efforts of municipalities on sewer networks can also be assessed based on the management of blockage related failures. Existing approaches to the management of blockages require a combination of proactive and reactive measures which have been described by authors such as Thomson (2008), DeSilva et al. (2011) andFontecha et al. (2016). However effective blockage management should be an optimized balance between proactive and reactive maintenance to maximize service outcomes at the lowest cost within operational budgeting constraints (DeSilva et al. 2011). ...
... Existing approaches to the management of blockages require a combination of proactive and reactive measures which have been described by authors such as Thomson (2008), DeSilva et al. (2011) andFontecha et al. (2016). However effective blockage management should be an optimized balance between proactive and reactive maintenance to maximize service outcomes at the lowest cost within operational budgeting constraints (DeSilva et al. 2011). Conventionally, reactive approaches are applied to assets with a perceived low consequence of failure, usually operated till failure occurs and associated with low recurrence blockages while proactive approaches are applied when the perceived consequence and cost implications of failure are considered to be high specifically high recurrence blockages According to Ugarelli et al. (2009) the expenditure on blockages are regular costs to municipalities. ...
Sewer networks are expected to operate with minimal or no interruptions. The complex nature of randomly occurring failures in sewer networks arising from blockages significantly adds to the cost of operation and maintenance. Blockages are significant due to sewage backup or basements flooding, resulting from their occurrence. Continuous performance assessment of sewer pipe networks is necessary to ensure a required level of service at an acceptable cost. This study provides insight into the performance of the sewer pipe networks by assessing the proneness of the network to blockages. Furthermore it draws inferences at a holistic strategic level of influential explanatory factors of blockage proneness, using data available in the Swedish Water and Wastewater Association's benchmarking system. Results indicate that medium sized municipalities are prone to at least 30% more blockages per km per year compared to other municipalities. A hypothesis of explanatory factors includes reduced flow volumes, design and flow depth. Flow velocities below self-cleaning velocity in sewer pipe networks, encouraged by sluggishness of flow are responsible for increased possibility for sediment deposition and accumulation in sewers leading to blockages. This is also exacerbated by the deposition of non-disposables (wet wipes, baby diapers, hard paper etc.), accumulation of fats, oils and grease in sewers and increased water conservation measures.
... Os sistemas de drenagem artificiais existem para resolver o défice de infiltração e, consequentemente, para evitar as inundações (DeSilva et al., 2011;Cherqui et al., 2015). As complexas redes de drenagem subterrâneas existentes nas áreas urbanizadas têm como objectivo retirar a água da superfície, evitando a sua acumulação. ...
... B. Chen e Liu, 2014). Também as rupturas de condutas na via pública e a obstrução das sarjetas por ramos e folhas de árvores ou outros detritos podem provocar inundações e/ou contribuir para a sua existência (DeSilva et al., 2011;Rudari et al., 2014;Cherqui et al., 2015). ...
Os diversos tipos de inundações podem distinguir-se pelos seus factores desencadeantes, processos hidrológicos, características hidrodinâmicas, extensão espacial e temporal e capacidade destruidora. Se as cheias progressivas e cheias rápidas são termos actualmente estabilizados cientificamente, o mesmo não sucede com as inundações urbanas. Actualmente assiste-se a uma multiplicidade de conceitos associados a este tipo de inundações, não permitindo uma correcta classificação das ocorrências. Neste artigo apresentam-se os conceitos e o enquadramento das cheias progressivas e rápidas, discutem-se as questões teóricas e metodológicas relativas às inundações urbanas e propõem-se os termos FREN (inundações relacionadas com a antiga rede de drenagem natural) e FUNN (inundações não relacionadas com a actual ou antiga rede de drenagem natural). Os danos materiais reportados às seguradoras no município de Lisboa no período 2000-2011 apontaram as FUNN como o tipo de inundação mais frequente (53% dos sinistros). Por outro lado, foram as FREN que geraram maiores consequências (58% das indemnizações). Os resultados obtidos demonstram a importância do relevo e das antigas linhas de água nos danos materiais resultantes de inundações.
... Futhermore, weak joints and cracks in old sewer pipes may lead to the intrusion of roots and other debris (Lu et al., 2000). Initially, intrusion of tree roots was identified as a great influence in spatial deposition (DeSilva et al., 2011;Ducoste et al., 2008) and Marlow et al., (2011) showed that blockages due to tree root intrusion can be of >75% for some utility areas in Australia. Since then, other solids such as disposable face masks, wet wipes, tampons, cotton buds, plastics, sanitary absorbents, grit and dirt have also been found in sewer networks. ...
Treatment of wastewater with high levels of fat, oil, and grease (FOG), produced by the growing number (annually 2%) of food service establishments (FSEs), is a major concern for water utilities. About 30-40% of sewer blockages are caused primarily by the formation of FOG deposits in sewer pipes, and an annual additional maintenance cost is required for sewer management. To manage FOG deposition, FSEs are required to recover the FOG at the point of generation by installing grease interceptors (GIs) before release to the sewer system. The successful control of FOG deposition is largely dependent on clear understanding of its complex properties, pre-treatment processes, deposition mechanism and public awareness. The objective of this study is to provide a comprehensive understanding of the physicochemical properties of FOG, including particle size distribution and their removal efficiencies by existing GIs. Nowadays, generation of FOG particles of ≤45 µm is increasing because of the increasing use of automatic dishwashers. Current hybrid processes which comprise pre-treatment prior to GI use are ineffective since they are unable to completely remove particle sizes of ≤45 µm. Hence, there is potential for these particles to be released into the sewer system and eventually cause blockages. This critical review discusses the characteristics of effluents, including the particle size distributions generated from automatic dishwashers and handwash sinks. It concludes by providing some case studies and a perspective of the future opportunities to develop a novel GI process integrated with pre-treatment to remove particles of all sizes, including colloidal particles.
... From the centre towards the northern peripheries in municipality A, except the northwest, pipes with increased sagging potential showed a stronger degree of influence, 11 -15% more compared to pipes with higher root intrusion risk and higher CCTV grades. This explains to some degree why pipes in this area may be plagued with structural problems which may result in increased sediment deposition and higher vulnerability with close proximity to trees, ultimately leading to the occurrence of blockages DeSilva et al., 2011;Torres et al., 2017). Reduced depth of pipes correlating to increased blockage propensity is also observed in this area. ...
Efficient management of sewer blockages requires increased preventive maintenance planning. Conventional approaches to the management of blockages in sewer pipe networks constitute largely unplanned maintenance stemming from a lack of adequate information and diagnosis of blockage causative mechanisms. This study mainly investigated a spatial statistical approach to determine the influence of explanatory factors on increased blockage propensity in sewers based on spatial heterogeneity. The approach consisted of the network K-function analysis, which provided an understanding of the significance of the spatial variation of blockages. A geographically-weighted Poisson regression then showed the degree of influence that explanatory factors had on increased blockage propensity in differentiated segments of the sewer pipe network. Lastly, blockage recurrence predictions were carried out with Random Forest ensembles. This approach was applied to three municipalities. Explanatory factors such as material type, number of service connections, self-cleaning velocity, sagging pipes, root intrusion risk, closed-circuit television inspection grade and distance to restaurants showed significant spatial heterogeneity and varying impacts on blockage propensity. The Random Forest ensemble predicted blockage recurrence with 60–80% accuracy for data from two municipalities and below 50% for the last. This approach provides knowledge that supports proactive maintenance planning in the management of blockages in sewer pipe networks.
... Sediment transport in sewers and sewage networks have been the topics of a few studies in recent years due to some concerns associated with the pollution to watercourses, blockage, and surcharging (DeSilva et al. 2011). In general, the sediment deposition occurs occasionally in sewers as a result of the intermittent nature of flow (Ghani 1993; Azamathulla et al. 2012). ...
In this study, two nature-inspired optimization techniques such as firefly algorithm (FA) and butterfly optimization algorithm (BOA) are combined with adaptive neuro-fuzzy inference system (ANFIS) and group method of data handling (GMDH) models for optimal prediction of the complex phenomenon of volumetric concentration of sediment (Cv) in sewer systems. Three different scenarios based on the methods of dimensional analysis and forward selection are implemented for determining the input structure of ANFIS, GMDH, and regression models (multiple linear regression, MLR; stepwise regression; SR) regarding 13 independent hydraulic and geometric input variables. Several statistic criteria including the root-mean-square error (RMSE), mean absolute error (MAE), Nash–Sutcliffe efficiency (NSE), index of agreement (AI), coefficient of determination (R²), and comprehensive synthesis index (SI) as well as Taylor diagram were used to further quantify simulating and predicting accuracies. In comparison with the regression models and two empirical equations, the results obtained by standard machine learning models (ANFIS and GMDH) were very promising. However, such integration of FA and BOA noticeably improved the performance of ANFIS (around 7% improvement in RMSE criterion) and slightly optimized the performance of GMDH (less than 1% improvement in RMSE criterion) in modelling the process of Cv prediction.
Graphic abstract
... FOG deposits are accumulated suspended solids in sewer systems and have an adhesive character. They can become firmly attached to interior sewer pipe walls, thereby substantially reducing and sometimes even completely blocking the wastewater flow (Desilva et al., 2011). They have a grainy, sandstone-like texture with high yield strengths (Keener et al., 2008) that require intensive cleaning activities such as hydraulic jetting (Dirksen et al., 2012;Mattsson et al., 2014). ...
Fat, oil and grease (FOG) deposits are an important contributor to blockages in building drainage systems. Such blockages bring undesirable financial, health and environmental costs, and thereby burden society. It is unclear to what extent the behavior of inhabitants, and more precisely domestic FOG disposal, affects the occurrence of FOG blockages. For this study, samples of FOG blockages were collected from building drainage systems (kitchen drains and lateral house connections) and analyzed. The results showed that the deposits were calcium salts of fatty acids. Dissimilarities between the network locations demonstrate that, even at short distance, in-sewer transformation processes occur. Surveys were conducted to reveal information about FOG disposal patterns. Three households showed a clear link between the type of cooking oils used and the type of deposits collected.
The present study deals with the problems of urban sewage system and trying to find out the geographical perspectives behind the same. For this assessment, previous literature has studied and analysed. Basically, the urban sewage system deals with the collection, treatment and disposal of the generated wastewater. Now a day, the continuous growth of population and the process of urbanization crating overload on the available service of the sewage system. The blockage, clogging, backwater, overflow etc are the major concern of the same. Resulted, many health issues, environmental pollution and hazards within the urban places. Dynamic nature of the city, lack of public awareness, challenging physical setup of the region and sewer construction, maintenance and cleaning issues, inappropriate collection and treatment, poor economy etc are the major geographical perspectives of the urban sewage system issues.
The shift of discussions on wastewater management to realize a circular water economy requires rethinking of how the existing systems are managed. The collection system, a physical infrastructure that collects and transports wastewater, is often overlooked in innovation studies in wastewater management. Hence, a review of the collection system is required to realize overlooked innovation points, especially those of its functions and configurations. In this paper, we highlight the possibility of the collection system to contribute to wastewater management, not only to collect and transport wastewater, but to treat wastewater through enhancing sewer self-purification. To realize this, a systems analysis of the forms and functions of the collection system was first conducted to see how the collection system supports different wastewater management systems. It was found that emphasis on the collection system's function to treat wastewater is beneficial because of the transition of wastewater management towards a circular water economy. Second, a scenario analysis of applying enhanced sewer self-purification technologies was conducted to determine communities which would most benefit from using the collection system to treat wastewater. The findings highlight that communities with as much as 100 cap ha-1, typical of urban peripheries, could have their pollutant load reduced to about half if the pipe length per capita is 5 m. It was seen in this study that while the collection system supports wastewater management by functioning to collect and transport wastewater, it can further be elevated into a treatment technology within appropriate localities and thus, contribute to a circular water economy.
The conveyance of wastewater in sewer pipes can be severely limited by the growth of plant roots, which can be controlled with herbicides. However, adding herbicides in sewer lines may affect downstream biological wastewater treatment processes. The effects of three herbicides (Dithiopyr, Penoxsulam, and Triclopyr) on the mortality of cottonwood tree roots and on downstream biological nitrification were determined. The results showed that Triclopyr achieved the highest root mortality (96%) followed by Penoxsulam (77%) and Dithiopyr (75%). At concentrations used at the point of application in sewer pipes, all herbicides caused nitrification inhibition and reduction in organic carbon removal in activated sludge. However, no inhibition was observed at the more diluted concentrations approximately equal to levels that may reach the wastewater treatment facility. Overall, Triclopyr appears to be the best performing herbicide with the highest root kill.
This literature review presents the state-of-the-art concerning sediment sewer transport modelling. After a description of solid particles found in domestic sewage and in storm water, the different steps taken into account in models are described: build-up over the catchment, washoff by rainfall, transfer through gully pots, transport, deposition and erosion in sewer pipes. For each step, several modelling approaches are presented with their basic equations. The paper ends with a short presentation of some models, and with some remarks about the comparison between models and field experimental data.
The invasion of sewer pipes by tree roots is a major cost to both the corporations managing urban infrastructure and to private landowners. There are a number of factors that may result in the growth of roots into and around the pipes. These include pipe material factors such as degradation of aging pipes and damage caused to pipes and environmental factors such as site conditions, tree proximity and tree species. Research into these issues will help in developing more efficient methods of controlling root invasion, benefiting both the management of sewer flow and the urban landscape. A study of root invasions in suburban Melbourne was carried out to examine relationships between site factors and root blockages. Common factors found associated with tree root blockages were Eucalyptus and Melaleuca species over 4m high within 6 m of sewers, pipe depth 2 m or less, rubber ring joined 150 mm diameter vitreous clay, 30 to 60 years old, soil types with sandy topsoils, and blockages occurring most frequently when temperatures and evaporation were at their lowest i.e. August to October. An experiment was conducted to evaluate chemical and physical treatments for preventing root growth in disturbed soil with high nutrient content and readily available moisture (modeling leaking sewers). Over a period of 177 days significant inhibition was achieved with the chemical treatments dichlobenil (278 g/m3 and 1392 g/m3), copper sulphate (1.5 g Cu/kg soil and 7.5 gCu/kg soil), oryzalin (1031 g/m3) and trifluralin (260 g/m3) and the physical treatments slaked lime (ratio of 10 soil:1 lime and 10 soil:5 lime) and cement slurry. The potential for the use of these treatments in areas where tree roots have damaged sewers is discussed.
Interference between trees and sewer systems is likely to occur in old systems and in cracked pipes. Factors that contribute to damage include old pipes with joints, shallow pipes, small-dimension pipes, and fast-growing tree species. Because roots are reported to cause >50% of all sewer blockages, costs associated with root removal from sewers is substantial. In smaller-dimension pipes, root removal every year or every other year is common. Major resources are put into replacement and renewal of existing pipes, which is sometimes accelerated because of root intrusion. Collapse repair costs are greater than new construction, but costs associated with root removal may be one-sixth the cost of pipe replacement/renewal due to roots. Major breaks and stoppages seem to occur more frequently in older systems than in new. Therefore, it seems worthwhile to carry out preventative maintenance of the older parts of the sewer system.
Why do tree roots penetrate pipes-and not only where the pipe is damaged? Root damage to the pipe connections of duly laid, intact pipes causes millions of damages per year. Engineers and biologists are searching for the reasons together. Their results are already turning past theories topsy-turvy and have consequences for laying pipes. Sewers are a rather inconspicuous property of cities and municipalities. But there are few things so important for the community. This becomes particularly obvious, if sewers do not work properly. A frequent cause are roots growing into the pipes.The estimated costs of repair and ultimately renewal of the pipes would rapidly exceed the total sum of a billion in Germany alone. While one can resort to bottled mineral water instead of drinking water, help out with aggregates in the case of electrical current and simply do without television occasionally, a defective sewage system is always an acute problem, that has to be solved quickly. We have investigated why roots represent a problem for piping systems at all in a cooperation project of the Chair for Systematic Botany and the Botanical Garden of the Ruhr-University with the IKT-Institute for Underground Infrastructure. Concepts to avoid this damage are to be developed, based on the accurate knowledge of what happens when roots penetrate. Sound precautions are particularly important, since it usually takes more than 10 years from pipe laying to the occurrence of damage and pipes should last for a long time (service life: 50 to 100 years). Biologists and underground engineers seem to be "natural enemies" in this respect, because one group argues, that nothing can happen, if the pipes are "decently" laid, while the other considers wood as an aggressive destroyer of the marvel of their engineering art. A biology student, who jobbed in underground engineering and returned to his academic roots with this problem, made the contact between both worlds.
Metham (sodium methyldithiocarbamate), applied alone or in combination with dichlobenil (2,6-dichlorobenzonitrile) in foam, was effective in killing roots of eucalyptus ( Eucalyptus camaldulensis Dehnhardt) or willow ( Salix hindsiana Benth.). An air-aqueous (19 to 1) foam of these herbicides was at least 20 times as effective as the aqueous mixture alone. Killing of the root with metham was rapid and extended above the lower treated portion, with the extent of necrosis resulting from translocation of the herbicide varying with concentration of metham that was used. The amount of the root killed with dichlobenil was limited to the treated area regardless of concentration. Four weeks were required to control the larger roots. Root killing with metham proceeded via both the aqueous and vapor phases. Results from labeling trees with ¹⁴ C-assimilates indicated that neither translocation nor accumulation were greatly affected by metham or dichlobenil except in the tissues actually killed. However, transport and accumulation into untreated roots were reduced for a few weeks by dichlobenil. Similar results were obtained with cotton ( Gossypium hirsutum L. ‘Acala’) treated with dichlobenil.
The recent California drought and attendant reduction in water utilization give a preview of the problems and potential benefits of reduced water use. The performance of sewer collection systems and treatment works operating at reduced flow conditions was analyzed. The effects of reduced water use on wastewater strength (biochemical oxygen demand, suspended solids, and nutrients) were evaluated from plant operating records of 14 treatment systems. The effects of reduced scouring velocities on sewer performance have been discussed with reference to sewer design correlation. Process performance of treatment plants has been analyzed with reference to a computer programmed process model. Operating problems and solutions are discussed. Potential benefits of reduced water utilization for existing and new systems are described.
Little is currently known about the nature, quantity or variability of WC derived sewer solids. This work describes results of a one week domestic WC usage survey in the UK. Specific attention is paid to solid production including faecal matter, toilet paper and sanitary refuse. Significant quantities of solids were found to be produced. The results illustrate distinctive diurnal usage patterns including the surprisingly low evening faecal related flush usage Weekend usage exceeded week day usage on average, but with reduced morning peaks. Differences between males and females usage were also noted, in particular the much larger toilet paper usage and sanitary refuse disposal associated with females.
Three sites with root intrusion problems in the City of Malmo were inspected to find different solutions to the problems. All sites had high maintenance costs due to the roots. Alternative measures for each site were selected. Each site was treated differently depending on the technical, aesthetical, cultural and economical values. At one site, pipes were relined, at another the trees were replaced with less aggressive species and at the third a decision is yet to be made. Tree roots entering sewer systems is a well- known phenomena. To be able to live and develop, a tree must have a sufficient soil volume and a good soil environment. One reason for the good environment for root growth around pipes is the condensation or accumulation of water outside or inside the pipe. The root tip follows the pipe and penetrates where there is a weakness. The design and type of the pipe is of utmost importance for root intrusion and the amount of root damage. Different materials can resist root intrusion differently. Older concrete pipes without rubber gaskets in the joints can resist root intru- sion the least and make up the majority of pipes with root intrusion problems. Concrete pipes with rubber gaskets in the joints have been found to have a higher resistance against root intrusion but are not fully reliable, especially not in older in- stallations. Pipes made of plastic (PVC) and fi- berglass (GAP) have, so far, been nearly resistant to root intrusion, if we disregard carelessness during construction, and the joints between these types of pipes and concrete pipes. Polythene pipes (PEH) are welded so there are no joints and no problems with root intrusion. The plastic pipes must have a very well-constructed and compacted gravel bedding, to get the stability to withstand a physical load, or there is a risk for deformation and cracking, with root intrusion as a result.
Australia cracked under the pressure of its longest recorded drought, with politicians and the public feeling the impact