Upgrading wastewater treatment facilities - Essay Example

Upgrading Wastewater Treatment Facilities The issue of wastewater treatment is a serious concern for municipals and city councils all over the world, especially the developing countries in Europe. The increased sensitivity in environmental conservation and the impacts of poor urban wastewater treatment to the environment led to adoption of stringent protection measures. The central focus of the new measures/regulation was protecting the environment from adverse effects of wastewater discharges from biodegradable and high-potential polluting industries. The European Economic Community and the European Commission embarked on designing a common regulation regarding urban wastewater treatment, as insufficient treatment of wastewater from a given state will have significant impacts on other member states (Vesilind, 2003:114). Consequently, industries and municipals were required to adhere to certain wastewater treatment policies that would ensure pollution and other adverse effects remain minimal, including the common primary settling and activated sludge. These regulations are still applicable, forcing majority of organization to upgrade their treatment facilities to more sustainable sanitation. This report discusses the issues that lead to non-compliance. The report further proposes the adoption of a recent technological innovation in chemically enhanced primary treatment (CEPT) as the best initial step in management and treatment of urban water waste through case studies approach (Marsalek et al., 2004:135). Introduction There have been numerous discussions on population growth in mega cities and urban areas in developing countries and the subsequent public health and water-related pollution. The central concern for the stakeholders has been whether these emerging mega cities should adopt the municipal wastewater treatment technology similar to that of Western Europe, whether there is need to adopt another approach that is more sustainable sanitation. There have been several attempts by concerned organizations and authorities to address the issues, including a report by the US National Research Council on the sustainable sanitation and water services for mega-cities. However, the 1996 report was short on specific, indulging in generalities for the larger part (Tchobanoglous, Burton, and Stensel, 2004:548). According to the authors, relevant water and sanitation professionals need to adopt a wider of sanitation technologies that enhance prevention of diseases from the multiple exposure routes and activities of wastewater. The selection basis for the most appropriate treatment technology should be the performance in promoting a healthy environment. The authors conclude the report by suggesting that the adoption of appropriate treatment technology would increase the cost-effectiveness of reuse and reclamation of municipal water waste. Appropriate wastewater treatment for developing urban cities has been a feature in the Water Science and Technology journal. About half the articles in the journal focus on analysis and definition of sustainability, while the remaining half deals with technology. However, most papers that address technology concentrate on very expensive, non-conventional collecting systems that incorporate separation, treatment, and disposal of faecal and liquid wastes through different processes. For instance, a paper by Somlyyody and Varis focuses on global urbanization and the affordability of sustainable sanitation (Roberts et al., 2010:125). The authors conclude that conventional the infrastructure of conventional urban wastewater management is neither transferable nor sustainable, particularly in the industrialized world. Nonetheless, the authors do not provide any specific solutions on sanitation and water problems facing megacities or affordable technological alternative. In yet another journal, Water Quality International, three academics exchange ideologies on sustainable sanitation. Keinath reiterates the world should consider the deliberate and direct reuse of water in the mega-cities. He bases his argument on the cost effectiveness of high standards of treating water, saying that it may be cheaper than exploiting distant subsurface and surface waters, proposing the development of membrane technologies and adsorption and oxidation processes. Okun seconds Keinath’s ideology, but argues that reuse of water would be limited to non-potable use such as agricultural irrigation as this only requires secondary treatment then filtration and chlorination without the need of new technology. Alaerts proposes another perspective, arguing that it would be less costly to reduce the water demand for households and factories. He argues that adoption of cleaner production technologies, stimulation of in-plan use, abolishing pollutant factories, and relocation to less-sensitive locations would be better than cleaning up effluent (Bochiniarz and Cohen, 2006: 178). He concludes by reasserting that that the central components of the scheme are cost-effective and innovative technologies. Unfortunately, the author does not outline these technologies, nor does he examine the possibility of abolition of industries in developing countries based no environmental concerns. From the above literature, North America and European water experts seem to lack any concrete and realistic upgrading proposals. This report presents a technological proposal that seeks to encourage the important discussion of appropriate treatment technologies that may ultimately solve the problem of urban sanitation in developing countries. Majority of urban areas have extensive sewerage systems that collect and discharge untreated water waste into coastal waters, shallow embayment, or adjacent rivers, thus contaminating them, except for a few cities such as Jakarta (Harleman and Murcott, 2005: 19). Sadly, only a small portion of the collected wastewater undergoes treatment, normally in secondary treatment plants using the conventional primary settling and activated sludge technique. These secondary plants are “token” treatment facilities. As such, they are prone to inadequate funding that may lead to improper operator training and maintenance. Another serious danger is biological upsets that may occur due to toxic industrial inputs. This report tries to define the most cost effective and efficient minimum treatment level required to promote public health, rather than seeking to describe advanced levels of wastewater treatment and the ultimate effluent end use. The first case study is Mexico City. Mexico City: A Case Study on the Need of Mega-Cities The Mexican Valley covers an area of approximately 1300 square kilometres, with more than 21 million inhabitants. The ground on which the city lies is a high plateau old lakebed, technically lacking a source of fresh water or natural drainage. Therefore, the city seems like the prime candidate for potable use or sewage reuse, as the large percentage of drinking water comes from distant low surface sources or deep ground water wells. According to statistics, the city produces about 75 meter cubed per second or raw sewage wastewater, which irrigates agricultural land of about 85000 ha in the state of Hidalgo (IRP, 2000:19). The raw wastewater comprises of high phosphorus, nitrogen, and inorganic nutrients, including helminth and coliforms eggs, debilitating parasites that with a high concentration of about 250eggs/L. Since the valley has poor soil, the nitrogen, phosphorus, and inorganic materials present in the raw wastewater greatly improve crop yields. In 1997 for instance, tomato yields increased by 94%, onions 100%, and corns 150%, among others. Moreover, irrigated areas get distribution of 80kg/ha of nitrogen annually. Applying Keinath’s proposal for reusing sewage as potable water in Mexico City is difficult considering the cost of high-tech tertiary treatment required for even a significant fraction of the city’s raw sewage. The most significant problem in the use of raw sewage for agricultural irrigation is the high possibility of contracting parasitic and enteric diseases among the more than 100,000 population of agricultural workers in irrigated areas. Mexico City seeks urgently seeks to find a treatment solution that will protect the agricultural workers by inactivating pathogen and removing helminth eggs, while at the same time allows the use of nutrients and organics for irrigation (Vesilind, 2003:135). Drawing from the proposal of Okun, reuse of sewage for irrigation is important, but it needs secondary treatment before disinfection. Western engineers and environmental planners share this ideology. However, the operating costs and capital for wastewater secondary treatment in Mexico City as well as other infrastructural present a challenge of determining whether the project is a necessity or a feasible option. Between 1993 and 1995, several environmental specialists advised the National Water Authority to adopt chemically enhanced primary treatment (CEPT) as a single-stage treatment technique that would result in high-level suspension of solid removal, especially helminth eggs, thus producing an economically and effectively disinfected effluent (Marsalek et al., 2004:138). Consequently, the Mexico City authorities based their full-scale and pilot tests on the proposal. Currently, the pilot plant studies on the combined use of CEPT alone and other high-rate sand filters are complete. The pilot studies indicate that CEPT is an effective method of removing helminth eggs on the rage of 2-5egs/L. Applying polishing sand filters insure that the effluent contains less than 1egg/L. The authorities did a cost evaluation comparison between the CEPT treatment strategy and the conventional primary and sludge treatment for various proposed treatment plants. For instance, the proposal for El Salto plant for treatment capacity of 15 meter cubed/s and mean flow of 5.2 meter cubed/s would cost about US$70 million including sludge disposal for a CEPT plant, while a conventional primary settling and activated sludge costs higher by a 1.85 factor. The Annual operation costs for the CEPT were US$4 million and US$7 million for the conventional plant. Moreover, the CEPT chemicals annual costs are higher due to the high costs of energy for secondary aeration tanks (Harleman and Murcott, 2005: 19). South California: A Retrofitting CEPT Case Study The enactment of Ocean Protection Plan in 1985 by California state authority required all treatment plants that disposed their waste into the ocean to maintain at least a 75% removal of suspended solids. During this timeline, the four largest treatment plants in Southern California used conventional primary treatment; three used partial secondary treatment, while one used primary treatment. Rapid population growth meant that the plants dealt more than the initial design capacity, leading to poor performance of the plants. Consequently, the operators turned to trivalent metal salts for potable water treatment process, which enabled them to increase solid removal percentage by flocculation and coagulation (Bochiniarz and Cohen, 2006: 146). The operators retrofitted their treatment plants to accommodate CEPT treatment more efficiently and cost-effectively. The use of physical-chemical treatment technique is a century-old technology. However, environmental professions were quick to disfavour that technology because the lime, the primary chemical used, produced higher volumes of additional sludge. However, the 1985 scenario in California used another approach: the plants used low dose ferric chloride as the primary coagulant (approximately 25mg/L) in combination with a tiny amount of anionic polymer as the flocculants (approximately 0.2mg/L). Consequently, the plants experienced improved treatment efficiency with a marginal increase in the primary production of sludge because of increased removal of solids (Roberts et al., 2010:118). After the CEPT retrofit, the overloaded San Diego conventional primary plant increased suspended solid removal by 85%, BOD removal by 55%, and phosphorus removal by 85%. Furthermore, the pollutant removal efficiency of CEPT at average surface overflow was about 4.5m/h, almost three times higher than that of primary settling tanks. In the history of the US, San Diego has a unique history in the treatment of urban wastewater (IRP, 2000:19). The city was under enormous pressure to comply with Environmental Protection Agency requirements of adding another costly secondary treatment plant. Nonetheless, a portion of the officials queried the prospect of using US$2 billion to add a small percentage of BOD removal to and already clean CEPT effluent discharged through a long ocean outfall. Scribbs scientists supported their queries, which led to a review of management of wastewater in coastal urban areas by the National Academy of Engineers. After the conclusion of the study, Congress waived secondary treatment waiver for San Diego, giving the City’s authority the permission to complete CEPT treatment at Point Lama as well as build a water reclamation plant that would target 15% of wastewater for land reuse. After implementation of CEPT, several other plants doubled their secondary flow capacity, such as Hyperion facility in Los Angeles City. This was a result of reduced BOD loading to secondary stage, as well as the easy solubility and oxidization of the BOD remaining in the effluent of CEPT. The earliest use of CEPT in North America was eminent in several primary plants in Canada in 1980s. The main reason for using CEPT was initially to reduce the large discharge of phosphorus into the Great Lakes. In Europe, the CEPT process goes by another term, “direct precipitation.” For instance, Norway uses a high dose of metal salt coagulant (about 100-250mg/L) to meet the phosphorus removal requirement of 95%, without biological treatment (Hahn, Hoffmann, and Odegaard, 2007:381). In recent cases, France and French Canada promoted high overflow rates chemical treatment using lamella plates. The result is an expensive but compact treatment plant that can occupy congested location in urban areas, because of secondary clarifiers’ elimination. CEPT Experience in Hong Kong In 1994, Hong Kong’s British government had a problem with the collection and treatment plans of sewage from Hong Kong Island and Kowloon, densely populated areas. The government’s long-term plan was to build a conventional primary treatment plant near Stonecutters Island (SCI) and a long ocean outfall system for effluent discharge into the southern waters. However, the mainland was against the treatment plan, arguing that it would be inadequate and that the possibility of pollution export to Chinese territorial waters was high. Therefore, the British government appointed an International Review Panel to device a solution. The reports from the panel gave three recommendations (EPD, 2001:19). First, upgrading the treatment process at SCI to CEPT was necessary. Second, a comprehensive CEPT process pilot study. Third, postpone of the long outfall. Consequently, the government implemented the proposals, upgrading the SCI to CEPT and reducing by two-thirds the number of settling tanks by taking advantage of a higher rate of surface overflow. By 1997, the world’s largest CEPT plant was complete, having an average flow of 20cubed meters/s and a maximum capacity of 40 cubed meters/s. According to operating data from the CEPT project, suspended solids removal was in the order of 85%, with 74% for BOD at a small dosage of ferric chloride (10mg/L). Moreover, the surface overflow rate was about twice that of conventional primary treatment. An added advantage was perhaps the use of seawater for toilet flushing. The success at SCI led to the appointment of another International Review Panel to address the treatment and collection of all sewerage from the Island of Hong Kong and meet ammonia water quality standards. The government plans to implement the recommendations from the panel, which may save up to US$1 billion (EPD, 2001:19). Impediments Despite the cost-effectiveness and efficiency of CEPT, the technology is not popular and used widely. There are several reasons that may explain this phenomenon. First, the plant operators who did the California CEPT upgrades were discreet such that there is little technical literature that highlights their results. Second, the fact that CEPT research cannot be done in a university laboratory generically means that there are few basic research papers. Pilot and bench-scale plant tests may only occur at the actual site in order to determine accurately the coagulant dosages and chemicals. Third, majority of operators believe that use of chemicals in treatment results in the production of too much sludge. Nonetheless, low chemical dosages result to about 10 to 15% additional sludge than that produced from removal of suspended solids (Vesilind, 2003:95). Fourth, majority of private design engineering firms are reluctant to implement practically new approaches. According to a recent survey by the American Consulting Engineers Council, three-quarters of engineers are wary of suits that result from failure of innovative technology. Therefore, this acts as the main reason for the past practice continuity. Fifth, firms get more profits when designing new plant expansions than upgrading and retrofitting existing plants with CEPT. Nonetheless, many countries in Europe are continuously testing and implementing CEPT technology in treatment plants. The central objective is to promote public in a cost-effective manner through the construction of minimum level wastewater treatment that allows effective deactivation of pathogens and removal of pollutants. CEPT provides minimal cost per unit volume of treated wastewater primarily because it has a relatively higher surface overflow rate as compared to conventional primary treatment. Moreover, CEPT technology does not hinder future biological upgrades. Rather, it ensures that subsequent biological treatments are efficiently small in both cost and size (Shi, 2011:31). Merits of CEPT First, CEPT technology only requires a small amount of flocculants polymers and coagulant salts to produce single stage, highly efficient treatment process that is better in terms of organic carbon and suspended solids removal than conventional primary treatment. It is also more convenient in energy consumption and phosphorus removal than the latter (Tchobanoglous, Burton, and Stensel, 2004:635). Second, CEPT results in increased treatment removal and capacity efficiency because of enhanced settling. This is evident from the retrofitting of California’s conventional primary plants, highlighting the cheap and fast upgrade to overloaded plants. Third, new CEPT plants may capitalize on the enhanced settling advantage to reduce settling tanks and increase surface overflow rate. In Mexico City for instance, the operating and maintenance costs and capital (including handling of sludge) for CEPT were estimated at 55% of the cost for secondary biological treatment and conventional primary. Four, disinfection of CEPT effluent is more efficient than that of conventional primary effluent. This is very important especially in preventing public health problems resulting from contamination of water supply (Marsalek et al., 2004:142). Five, the resultant sludge from CEPT is easy to dewater and process. The sludge that results from the CEPT technique is about 10 to 15% higher than that resulting from removal of suspended solids. Last, CEPT is an appropriate and effective first stage treatment process, and biological treatment may follow based on justification and affordability. Conclusion The main water-related environmental concern eminent in urban areas of most developing countries is public health. Receiving water and drinking water sources are often contaminated inadequately treated wastewater effluents. Despite the presence of conventional primary treatment, disinfection of effluent is not effective (Shi, 2011:27). The main objective of upgrades to existing treatment facilities and initial investment wastewater treatment should be cost-effective, high-flow technology such as the CEPT, which will provide high removal levels of suspended solids, thus enabling effective inactivation of pathogens through disinfection. Environmental experts must not perceive the issue as a challenge between chemical and biological nature. Indeed, primary chemical treatment is most cost-effective initial treatment step, and biological treatment processes may follow, if justified and affordable. Literature on the subject indicates that most studies were based on short-term ad hoc strategies, with little effort and time for research an exploration. Despite the evident success of CEPT, there is need for further based on long-term field studies and research at different treatment plant (Harleman and Murcott, 2005:19). By 2050, the adoption of CEPT technology may lead to enactment of more stringent environmental regulation as the technology seem to favour low pollution rates. However, there is need for further research on improving the efficiency of CEPT technology through mixing flocculants and coagulants in a controlled environment. Bibliography Bochiniarz, Z and Cohen, G. (2006). The Environment and Sustainable Development in the New Central Europe. Oxford: Berghahn Books. EPD. (2001). A Clean Harbor for Hong Kong. Retrieved on March 19, 2012, from www.info.gov.hk/ssds.review Hahn, H., Hoffmann, E., and Odegaard, H. (2007). Chemical Water and Wastewater Treatment. London: IWA Publishing. Harleman, D., and Murcott, S. (2005). An Innovative Approach to Urban Wastewater Treatment in the Developing Countries. Retrieved March 19, 2012, from http://cd3wd.com/cd3wd_40/ASDB_SMARTSAN/CEPT-Debate-1.pdf IRP. (2000). Review of Strategic Sewage Disposal Scheme for Hong Kong Harbor. Retrieved on March 19, 2012, from www.info.gov.hk/ssds.review Marsalek et al. (2004). Enhancing Urban Environment by Environmental Upgrading and Restoration. Dordrecht: Kluwer Academic Publishers. Roberts et al. (2010). Marine Watewater Outfalls and Treatment Systems. London: IWA Publishing. Shi, C. (2011). Mass Flow and Energy Efficiency of Municipal Wastewater Treatment Plants. London: IWA Publishing. Tchobanoglous, G., Burton, F., and Stensel, D. (2004). Wastewater Engineering: Treatment and Reuse. New York: McGraw-Hill. Vesilind, P. (2003).Wastewater Treatment Plant Design. London: IWA Publishing. Read More