Wastewater Management System for a Remote Community - Essay Example

Wastewater Management Introduction According to Kadlec (2009), scar of water and contamination of ground and surface water are one of the most profound environmental problems in the modern world. Current water resources’ management practices are inadequate to meet the demands of the rapidly increasing population and the resulting surge in water consumption. In the rural areas, inefficient and insufficient planning has also led to serious contamination of local watersheds. From an overall perspective, Henze (2005) is of the opinion that wastewater management at all levels in rural areas is inadequate. Sewage systems that are poorly maintained or virtually non-existent, untreated animal wastes, landfills that are poorly regulated and rising levels of industrial effluents are some of the reasons and issues behind contamination and wastewater generation. In fact, untreated sewage often tends to flow into the streets in rural areas (especially in developing countries) and can run into agricultural fields contaminating the clean water and food sources. This paper will describe two distinct conceptual models for wastewater management and evaluate relevant issues such as water conservation, reuse and sustainability. Thereafter, the best model among the two shall be elaborated further and include a detailed description of the inherent wastewater management scheme. The paper also includes a detailed stakeholder analysis to ascertain the various issues affecting and influencing each stakeholder who is either involved or affected due to the prescribed wastewater management scheme. Models for wastewater management Model 1 The first model for wastewater management consists of a pilot plant system made up of an ASB (up-flow anaerobic sludge blanket), a CW (constructed wetland), SF (Intermittent sand filter) and AVB (Passively aerated vertical bed). This treatment model is highly flexible and can accommodate various wastewater treatment combinations. Each of these components is described below (Henze, 2005): Anaerobic sludge blanket (ASB): the reactor segment of the plant is conical in shape and does not contain any gas separators for any initial treatment upon preliminary sedimentation. The average working volume of the reactor is 7.5 m3 and has a surface area of 8 m2. The ASB concept has been devised, developed and applied in many parts of the world, especially in the rural regions of developing nations such as China and Brazil (Rofe, 2004). Aerated vertical bed (AVB): For the current consumption levels of 200 L/d per house, a passive aeration system consisting of four vertical beds can be developed through an operational sequence consisting of fills and draws. Each individual unit normally has a diameter of 2.5m and a height of 2.4m. The unit is filled with two different types of gravel namely the small variety as the upper layer. An aeration vent runs across this upper layer and supplies air to the underlying coarse gravel layer below. The influent is thus distributed evenly at the top of the vertical bed and drained effectively along the lower levels (Qasim, 2008). The intermittent outflow can be regulated using an electrical valve. Each unit was filled sequentially with gravel of decreasing sizes with a maximum of 16mm and a minimum of 3mm. Previous studies by Duncan (2006) have emphasized the importance of passive aeration especially for units containing smaller gravel while such requirement is less stringent for larger gravel sizes owing to wider gaps for percolation in the latter case. Fig 1: Schematic for passively aerated vertical bed (Source: Kadlec, 2009). Wetland (CW): a 140 sq. Meter wetland with a sub-surface flow should be constructed with a length to width ratio of 4:1 and a depth of around 0.7m. The medium can be composed of gravel with an average diameter of 2cm and a mean void spacing of 0.5. A manifold accompanied with several drip-irrigation outlets can be used for distributing the influent. An inlet with a width of 1m is prepared with stones of sizes ranging from 5-12 cm and planted with the species ‘Phragmitis australis’ (Chememisinoff, 2005). Based on previous estimates by Matsuo (2001), an organic loading of up to 8g BOD/m2 can be achieved using this construction. Sand Filter (SF): an intermittent sand filter of height 2m and radius 1.2 m is used in the plant system. The filter is made up of two sand layers with particle sizes ranging between 0.3 and 1 mm. The bottom of the filter is supported by a couple of layers made up of gravel and the drainage layer consists of rocks between 30-60mm in diameter. The system also consists of a gravity dosing tank that is set on high ground to allow appropriate dosing and distribution. The distribution network can be constructed using PVC pipes of around 0.5-0.7 inches in diameter and should contain around 6-8 orifices of about 4mm each. Tay (2006) says that to ensure an efficient distribution of wastewater along the surface of the filter, it is important to maintain a constant ratio between the quantity of orifices and the area of the sand surface. The primary influent for the above treatment system is the wastewater from the isolated rural community being developed. As is common with most newly built wastewater system, the control during initial phases of the project can be limited. This can result in wide variations in the characteristics of influents in terms of the concentration of suspended solids and COD. The results indicate that the combination of extensive and semi intensive treatment systems is an efficient way for treatment and reuse of wastewater in rural areas (Loubinus, 2007). Specifically, it was found that the up flow anaerobic sludge blanket (UASB) bioreactor system can be a good alternative for anaerobic ponds, significantly reducing the required area with better performance. The effluent of the UASB can be fed directly to either intermittent sand filter (ISF), or constructed vertical or horizontal wetlands. Model 2 The second model utilizes a rather conventional approach to wastewater treatment and management. In small, isolated and rural communities, wastewater treatment is usually achieved through the installation of septic systems, collection systems that discharge all effluents into water bodies and through municipal lagoons that are drained on an annual basis. As the community being developed in this case is isolated, it is assumed that there is no access to either water bodies or municipal services which eliminates the inclusion of the last two methods of wastewater management. The key to installing a treatment system for a rural, isolated community as in the present case is to treat and disperse all effluents at the source and minimize operational and maintenance costs (Arceivala, 2006). It must also be pointed out that installing complex and sophisticated wastewater treatment plants for rural communities may be expensive and infeasible. Some isolated communities have devised innovative ways to treat their waste. For example, several communities in the Arctic region have preferred methods that allow reuse of wastewater as freshwater is an expensive resource in this region. This is achieved by depositing the wastewater in a septic tank, filtering it and treating it with ozone methods for disinfection and non-consumptive purposes (McClelland, 2008). These methods allow such communities with limited access to water to reuse as much as 60% of wastewater for sanitary and laundry purposes. Fig 2: Septic tank system. (Source: Arceivala, 2006) The diagram above shows a septic tank in detail. The solid waste matter settles at the bottom in the septic tank while a scum is formed at the top in a manner that is similar to the settling tanks used in urban wastewater treatment facilities. The water, separated of solid matter through compartments and screens, is led into the drain field. The sludge matter retained within the tank is partially decomposed by bacteria present inside (Diane, 2004). The water that enters into the drain field begins to percolate into the soil. As long as the microbes present in the soil are adequate, the pollutants present in the water can be digested and the water can be free from most types of bacteria and viruses. Moreover, the water purified by this process is also removed of excess nutrients by the time it reaches the underlying water table. Fig 3: Contents of a septic tank system (Source: Arceivala, 2006) In the current case where the soil has a limited permeability, an alternative approach can be adopted to ensure that the water sources do not get contaminated. This method can make use of peat, sand and plastic instead of soil. The importance of using this alternative method arises from the fact that over half of the wells present in rural areas are contaminated primarily from septic tanks present nearby. The US Centre for Disease control and prevention states that septic tanks should be at least 15m from any nearby well although this may increase depending on the nature of the soil (Duncan, 2006). A recent study by the United States Geological survey in 2008 established that over 37% of wells in the state of Pennsylvania were close to sewer lines and viruses were detected in over 15% of the wells surveyed (Kadlec, 2009). The study established that deficiencies in the required sizes of absorption fields were the major reason behind the inability of septic tanks in achieving full efficiency. Thus, it is necessary to determine the most appropriate size for the drain field by taking into consideration several parameters such as the volume of daily influent flow and the type of soil. Further, any rural location depending on a septic tank system for wastewater treatment must maintain it properly as any discrepancy in proper management may lead to the leakage of pollutants and contamination of nearby land and water resources. Analysis of the chosen model From the above two models, it is obvious that the conventional method of using septic tanks for wastewater treatment will not be suitable in the current scenario as there are chances that every household may not have sufficient area to develop a drain field in conjunction with average daily usage. The proximity of the locality to the lake which serves as the only available source of freshwater combined with the likelihood of inefficient wastewater treatment may lead to the contamination of the former. As such, it is recommended to adopt the partially aerated vertical bed system due to several inherent advantages. Firstly, the reactor system provided by the AVB is capable of treating wastewater of high strength which can be a likely occurrence in a rural area assuming that the major economic activity is agriculture. In such circumstances, wastewater from agricultural processing activities can have such high concentrations and may need special treatment beyond the capabilities of a septic tank system (Rofe, 2004). The treated wastewater is also highly suitable for irrigation purposes and does not consume any electricity. Further, the maintenance required for managing the AVB is minimal and the system aids in sustainable development through waste minimization and generation of valuable compounds that can be reused. For example, the sludge separated from the wastewater can be reused as a composting material. It is estimated that based on water consumption of 200L/d and the average maximum presence of 8 persons per household, the mean influent discharge per day is in the range of 120-140 L/d even after taking into account that about 30% of clean water is used for external purposes. The quantity of wastewater that can be treated using this technique and reused is in the range of 52-64% depending on the concentration of solid wastes in the wastewater (Matsuo, 2001). The most striking aspect of the AVB is the quality of wastewater treatment. The average removal efficiencies of BOD and TSS concentrations were over 90% with a remaining effluent concentration of 15mg/l for BOD and 20 mg/l in the case of TSS (Rofe, 2004). The details of various sections and components of the AVB model can be found in the preceding section under the title ‘model 1’. The features described above make the AVB treatment model an efficient technique for wastewater treatment in the rural location under review. Specifically, the bioreactor system used for treatment is a viable alternative to anaerobic ponds and requires lesser areas without compromising on performance. Further, the system is highly flexible depending on the options available to individual households wherein the effluent from the ASB can be fed into an AVB, a constructed wetland or an intermittent sand filter depending on individual availability and feasibility (Arceivala, 2006). The recommended option amongst the ones available under the reactor model is to use a combination of the ASB and AVB as this arrangement is found to require minimal land area, reduce water loss and prevent the increase of salt concentration in the soil due to the effluent flow. Further, this method involves low costs for operation and management and does not require extensive oxygen supply for nitrification or decomposition of organic matter. Managing the stakeholders A number of issues have been identified that need to be discussed with relevant stakeholders. The primary stakeholders in this case are the local residents, the developer of the rural location and the local administration that enforces regulation and compliance within the legal framework of the region. The adoption of any new wastewater treatment plan is associated with additional costs for homeowners which differ based on the kind of system installed. It is necessary to determine whether any government subsidies are available that can at least partially waive the installation cost and encourage homeowners to adopt sustainable and non-polluting means of wastewater management. In terms of risks to public health, there is a widespread need to ensure that proper safeguards are in place when installing any proposed treatment system and that the local residents are thoroughly educated on issues like optimal level of water usage, proper treatment methods etc. This consideration assumes significance given the need for onsite infrastructure unlike a centralized system common in urban areas (Matsuo, 2001). The chances of risks to public health are also prominent in the rural context due to closer contact of residents with untreated discharges and treatment facilities. Thus, there is a need to evaluate the potential health vulnerabilities that residents may encounter due these issues and adequate steps must be taken to prevent any unhealthy practices. As the residents have opted for managing the wastewater individually, there is a need to undertake training sessions for educating them on proper maintenance of the treatment systems due to reduced user invisibility from related operations. Due to localized treatment, the residents will spend more maintenance hours on these systems and must be well versed with the intricacies and capabilities of these systems in order to ensure a continued availability of wastewater treatment (McClelland, 2008). In cases where individual land required for treatment is not adequate, households can combine components such as soil filters with others in close proximity to derive the combined benefit of proper treatment and reuse. References 1. Arceivala (2006), Wastewater Treatment for Pollution Control and Reuse. Chicago: McGraw Hill. 2. Chememisinoff (2005), Handbook of water and wastewater treatment technologies. London: Butterworth-Heinemann. 3. Diane (2004), Small Community Water and Wastewater Treatment. London: Routledge. 4. Duncan (2006), Domestic wastewater treatment in developing countries. Boston: Earthscan. 5. Henze (2005), Wastewater treatment: biological and chemical processes. New York: Springer. 6. Kadlec (2009), Treatment wetlands. New York: CRC Press. 7. Loubinus (2007), Rural wastewater treatment for individual homes. South Dakota State University. 8. Matsuo (2001), Advances in water and wastewater treatment technology: molecular technology, nutrient removal, sludge reduction and environmental health. New York: Elsevier. 9. McClelland (2008), Individual onsite wastewater systems. University of Michigan. 10. Qasim (2008), Wastewater treatment plants: planning, design, and operation. Chicago: Technomic. 11. Rofe (2004), Wastewater Treatment: Evaluation and Implementation: Proceedings of Water Environment. London: Thomas Telford. 12. Tay (2006), Biogranulation technologies for wastewater treatment. 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