Integrated, Decentralized Wastewater Management for Resource Recovery in Rural and Peri-Urban Areas
Abstract
:1. Introduction
2. Decentralized Wastewater Management
3. Sustainable Design of New Decentralized Wastewater Treatment Systems
3.1. Constructed Wetlands
3.2. Membrane Biological Reactors (and Related Technologies)
3.3. Anaerobic Digestion Systems
3.4. Sustainability of Wastewater Treatment Technologies
4. Sustainable Wastewater Collection and Transport
4.1. Source Control and Improved Sustainability
4.2. Vacuum Sewerage System: Benchmark of Sustainable Collection?
5. Discussion
Consequences of Decentralization
6. Conclusions
Acknowledgments
Conflicts of Interest
References
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Issue/Impact | Requirements | Notes |
---|---|---|
Health and Hygiene | Minimize human risk of exposure to pathogens and hazardous substances that could affect public health, from the point of disposal to the point of final discharge/reuse. | Some degree of disinfection should be provided in case of reuse or human contact. |
Environment and Natural Resources | In addition to pollutant removal effectiveness, resources for system construction and operation, as well as resulting emissions, must be considered. Degree of recycling and re-use from operation (e.g., returning water, nutrients, and organic material to agriculture), and protection of non-renewable resources (e.g., production of biogas) must be also compounded. | Receiving environment is crucial for technology selection. Site evaluation processes and assessment of its carrying capacity should be carried out. |
Technology | Functionality maximization, ease of construction, operation, and monitoring by local utilities are paramount in case of decentralized systems. | Robustness and/or vulnerability towards power cuts, water shortages, floods, etc., are important. |
Financial and Economic | Decentralized systems must relate to the capacity of local households/communities to pay for the system (including construction, operation, maintenance, and necessary reinvestments). | Systems should provide service without becoming excessive financial burdens on the users’ community. |
Socio-Cultural and Institutional | Socio-cultural acceptance, convenience, perception, impact on human dignity, compliance with the legal framework, and institutional settings must be considered. | Users must be informed and accept underlying practices, including those of reuse and recycle of resources. |
Aesthetics and Nuisance | Aesthetic impact should be reduced, as decentralized systems are usually closer to residential areas. Nature integration and ecological function or (on the other hand) mimetism or concealment should be included in design. Design and operation must take into account possible nuisance factors (i.e., odors) and prevent them. | Public is especially sensitive to highly subjective nuisance factors (odors rank highly among them). Good practices can reduce rejection risk. |
Issue Category | Septic Tanks (Imhoff & Other) | Constructed Wetlands | MBRs | Anaerobic Processes (UASBs) |
---|---|---|---|---|
Environment | ||||
Environmental protection | Removal of settleable organic matter. Partial removal of dissolved organic matter, practically no nutrients removal. | Effective in removing organic matter and, to a lesser degree, nutrients. | Quite effective in removing organic matter; also effective in removing some types of micropollutants and, upon proper setup, nutrients. | Effective in removing organic matter, might need finishing stage. No nutrient removal, must be followed by post-processing for this purpose. |
Human and ecosystem health | Effluent needs post-processing, usually by land disposal (where allowed) or CWs. No significant disinfection performed. | Effective integration with existing ecosystems, little disinfection (must be followed by post-processing or tertiary disinfection stage). | Effluent highly compatible with discharge into surface waters. Depending on membrane, media characteristics can provide some degree of disinfection. | Effluent usually needs a finissage post-processing. Little disinfection performed. |
Resources conservation | Limited soil consumption (underground systems), low to nil energetic input, water is returned with partial treatment to groundwater (infiltration) or surface waters (usually after CW finissage). | Integrates treatment function with ecosystems, low energetic input; returns water to the natural cycle. | Reduced soil consumption for construction, high energy demand. Low conservation. | Reduced soil consumption for construction, low energy demand. Energy recovery. Effluent and excess sludge high in nutrients (could be used in agriculture). Sludge can be processed for nutrient recovery. |
Water reuse | Water is returned to the natural cycle with limited treatment. Possibility of groundwater contamination (organics, nitrates). | Water is returned to the natural cycle (ground and/or surface water). Possible losses for high evaporation in arid countries. | Effluent water of high quality can satisfy most non-drinking uses. | Effluent water can be used in irrigation or other local uses after adequate postprocessing. |
Nutrients and materials recycling | Bottom sludge containing nutrients must be periodically evacuated. Processing is necessary (e.g., composting) before recycling. | Nutrients are recycled into biomass. This must be periodically removed for recycling and proper CW functioning. | Process can be adapted for nutrients removal. Low excess sludge production. | No nutrient removal. Sludge can be postprocessed for nutrients removal, energy (e.g., biodiesel) or chemicals extraction. |
Energy/GHG emission | Low energy requirements. Anaerobic conditions may cause emissions of methane and CO2 in quantities that are not usually worth recovering. | Very low energy requirements and emissions. Low GHG emissions if anaerobiosis is avoided. | High energy requirements, with high, related GHG emissions. Possibility of other N-related GHG emissions. | Low energy input. Energy recovery as biogas (biohydrogen possible). Uncollected/dispersed methane is considered harmful GHG emission.Transformation of biogas to biomethane suggested is not enough local heat users. |
Economical | ||||
Investment costs | Minimal | Could be significant only for land area (and connection system to users). | High. Although footprint is lower than a traditional AS and equivalent CW, membrane cost is rather high. Needs connection system to users. | Low, especially for physical infrastructure. Needs connection system to users. |
O and M costs | Minimal (only periodic evacuation of sludge required). Some users “feed” these systems with lyophilized biomass to improve org. matter degradation. | Low (some pumping to facility probably required). Biomass removal and disposal. Personnel do not need to receive complex training. | High, due to energy costs and periodical membrane media substitution/ cleaning. Personnel need relatively complex training. | Low. Personnel do not need complex training. |
Efficiency (technology) | Low efficiency, low cost solution. Usually adopted as a first level of sanitation in developing countries. | Cost of technology per unit organic pollutant removed is low. Robustness of technology is good. | Cost of technology per unit organic pollutant removed is medium. Robustness of technology high (if proper maintenance performed). | Cost of technology per unit organic pollutant removed is low. Robustness of technology medium-high. |
Residuals management | Excess biomass (sludge) and scum must be periodically removed and disposed. Depending on quantities, could be processed for recovery of energy/material. | Biomass must be periodically removed and disposed. Depending on actual vegetation, could be processed for recovery of energy/material. | Low excess sludge production, some collection and disposal required. | Very low excess sludge production. |
Population served | Very low-sophisticated technology can be built and managed by poorly-skilled local population, providing occupation and growth. | Low sophisticated technology can be built and managed by poorly-skilled local population, providing occupation and growth. | Highly sophisticated technology; structures can be built by medium-skilled local population, providing some occupation. Operation will permanently require skilled labor. | Somewhat sophisticated technology; structures can be built by medium skilled local population, providing some occupation. Operation will permanently require some skilled labor. |
Social | ||||
Public health | Must not be directly accessible. Can be supplemented by disinfection treatments (solar, etc.). | Facility must not be directly accessible by citizens. Not much disinfection provided by this technology. Could be supplemented by solar stage. | Disinfection provided to a certain degree. Removal of micropollutants (including some pharmaceuticals and endrocrine disruptors) possible. | Not much disinfection carried out by the process. Further post-processing required. |
Human settlement | Applicable in rural settings, with enough separation from people served. No lower/upper limit to service size. Should avoid direct nuisance effects (odors, insects, etc.). | Applicable mostly in rural/peri urban settings, with separation (distance) from people served. No lower/upper limit to service size (except area availability) Should avoid direct nuisance effects (odours, insects, etc.). | Applicable in all settings (urban to rural) once provisions are made to avoid possible nuisance to population served. | Applicable in all settings. In urban settings, it should be preferably contained to avoid nuisances. |
Nuisance and aesthetics | Predictable nuisances may include odors from improperly built systems, insects, and pests (rats, birds, etc.). Aesthetics not a problem as these systems are usually completely underground. | Predictable nuisances may include odors, insects, and pests (rats, birds, etc.). Aesthetics can be improved by proper design and landscaping. | Nuisances can consist of odors, noise, and traffic. Odors can offend resident population and be source of unacceptance and complaint. Appropriate measures should be introduced since design stage. Aesthetics can be improved by landscaping and mimetization. | Nuisances can consist of strong odors, noise and traffic. Odors can offend resident population and be source of unacceptance and complaint. Appropriate measures should be introduced since design stage. Aesthetics can be improved by landscaping and mimetization. |
Planning | Proper, shared planning addressing the resident population’s concerns should be enacted since the first moment. Often, proper and open communication with stakeholders is the key for social acceptance. | |||
Operating fees | Extremely low. | Low. Can easily be supported by users. | Medium-high. Can be supported by motivated users with specific objectives of water quality (including recycling). | Medium-low. Can be supported by users. |
Government regulations | Not allowed any longer in some developed Countries. | Process can comply with basic w.q. (water quality) regulations. | Process can comply with advanced w.q. regulations. | Process can comply with most w.q. regulations. |
Citizens’ attitude | It could be well accepted in developing countries as a first-stage solution to basic sanitation. | As a general rule, citizens will usually support “natural” treatment methods, especially if they are convinced that no nuisance will follow. | Citizens tend to be wary of such “high-rate” processes, as they might fear that their control will not be as spotless as initially declared, with the possibility of nuisances arising. Operator’s prior reputation will help. | Notwithstanding the initial perspective of resource recovery attached to this technology, citizens tend to be wary of similar processes as they might fear that of nuisances (esp. odors) could arise. Operator’s reputation demonstrated with prior success cases will help. |
Remarks | It could constitute the basic component of a decentralized system followed by finishing and disinfection processes. | CWs main limitation is related to the surface area needed for construction. CWs are better compatible with conventional-type collections systems with limited or no source separation and relatively diluted wastewater. | MBRs main limitation is related to their status of aerobic technology (energy-intensive operation). Anaerobic MBRs are being developed, but their cost puts them at a disadvantage compared to other anaerobic processes such as UASBs. A second limitation of membrane processes is the cost of the filtration medium and its fouling tendency in time, reducing operating life. Compatible with source separation (esp. with the greywater component) and moderately water-reduced systems. | UASBs require less surface area compared to CWs, and much less operating energy than MBRs. The greatest advantages of UASBs is their construction and operational simplicity, and the possibility of energy (biogas, biohydrogen) recovery. Originally mostly used in warm regions, their applicability at low temperatures (down to 10 °C) has nevertheless been shown. Effluent could be processed for nutrients recovery. |
Source | Volume (L/cap/d) | TSS Range (mg/L) | COD Range (mg/L) | N Range (mg/L) | P Range (mg/L) | Metals & Micropollutants | Pathogens |
---|---|---|---|---|---|---|---|
Blackwater | 1–7 | 16,000–125,000 | 5000–93,000 | 1500–16,000 | 500–3000 | High | High |
(~10 mg/cap/d) | |||||||
Greywater | 70–150 | 100–800 | 200–450 | 6–22 | 0.4–8 | Very High | Low |
(10 mg/cap/d) | |||||||
Urine | 0.5–2.5 | 15,000–30,000 | 4000–11,000 | 1800–18,000 | 200–4000 | Very low | Medium–Low |
(<1 mg/cap/d) |
Application | Comments | Additional Infrastructure Required |
---|---|---|
Agriculture (irrigation) | Irrigation is the most popular water reuse application in the world. Appropriate treatment practices are determined by local pedology, crops, and legislation. Usually seasonal. | Distribution system, pumping. |
Lanscaping (irrigation) and surface storage (ponds) | Irrigation of parks and residential greens, golf courses, cemeteries; roadside vegetation is another very popular water reuse. Surface storage (vegetated ponds) of partially treated water can be used for the creation of aesthetic value in peri-urban housing developments when seasonal irrigation is not needed. | Distribution system, pumping, creation of artificial basins. |
Other urban (non irrigation) | Street washing, fire protection, air conditioning cooling, car washing, and commercial laundering are examples of urban non-irrigation applications. Non seasonal. | Distribution system, pumping, and storage (can be surface ponds above). |
Environmental and recreation | Wildlife habitats and wetlands, and river flow enhancement/augmentation (may contribute to indirect potable use). Creation of lakes and ponds for recreational use. Non seasonal. | Distribution system, pumping, creation of artificial basins. |
Groundwater recharge | Restoration of groundwater levels and control of saltwater or blackish water intrusion into freshwater aquifer. May contribute to indirect potable uses. Non seasonal. | Distribution/infiltration system. |
Industrial applications | Cooling uses in power plants, oil refineries, and manufacturing facilities. Use as process water after suitable treatment. | Distribution system, pumping, and additional treatment (process water). |
Domestic and commercial (toilet flushing) | Reclaimed greywater can be used, after preliminary processing, for toilet flushing or outdoors surfaces cleaning. Non seasonal. | Dual distribution system, pumping, and additional disinfection treatment. |
Direct potable use | Documented direct potable reuse applications exist in the capitals of Namibia, Windhoek, and Singapore. Tertiary-treated wastewater is discharged to surface reservoirs, where it mixes with freshwater and undergoes heavy RO and disinfection supply-grade treatment before being fed to the water distribution system. This solution is being also studied in other water-deficient areas (California). Requires ample consensus on the part of users. Non seasonal. | Tertiary wastewater treatment, surface storage, advanced drinking-grade treatment, and pumping. |
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Capodaglio, A.G. Integrated, Decentralized Wastewater Management for Resource Recovery in Rural and Peri-Urban Areas. Resources 2017, 6, 22. https://doi.org/10.3390/resources6020022
Capodaglio AG. Integrated, Decentralized Wastewater Management for Resource Recovery in Rural and Peri-Urban Areas. Resources. 2017; 6(2):22. https://doi.org/10.3390/resources6020022
Chicago/Turabian StyleCapodaglio, Andrea G. 2017. "Integrated, Decentralized Wastewater Management for Resource Recovery in Rural and Peri-Urban Areas" Resources 6, no. 2: 22. https://doi.org/10.3390/resources6020022