Is greywater recycling sustainable
Excellent article by Timony Siebert, Environmental Consultant for Talbot & Talbot
Access to water is an urgent issue facing Southern Africa; nearly 100 million people lack adequate access to water. While access to water has become a global concern, solutions remain local, as scarcity varies from region to region depending on the combination of socio-economic factors, climate fluctuations and infrastructure.
Water scarcity is, however, on the rise. Scientific projections draw attention to how predicted changes in rainfall, limited resources for adaptation and lack of institutions and/or capacity to regulate river and stream flow are likely to leave communities extremely vulnerable.
Climate change is also predicted to have profound implications on water resource supplies. Modelling by the Council for Scientific and Industrial Research (CSIR) shows that regions in Southern Africa will become hotter and drier over the next 50 to 100 years, putting farms, industry, domestic water supply and natural ecosystems at risk. Combined with the social changes affecting demand, quality and supply, these impacts have the potential to seriously disrupt water availability. As climate changes start to take effect, individuals and communities will take actions to respond to and accommodate changes in water availability. This may be by expanding supply in a way that reduces climate variations, or addressing water use and demand to reduce the exposure to climatic variability and extremes.
Such implications are especially pertinent for communities and countries that rely heavily on water for their GDP and daily subsistence. More than 70% of the Southern African Development Community’s population depends directly on farming – and overwhelmingly so on rain-fed agriculture. Agriculture already accounts for almost 70% of the global water diversion, and the pressure for agricultural production is not likely to ease, as food security is one of the major Millennium Development Goals. But with an emerging economy and rapidly growing population, the demand for water by municipal and industrial sectors in many cities in Africa is likely to increase the competition for water. It is expected that water that has historically been reserved for agriculture will be diverted to the urban and industrial sectors.
Growing global pressures for freshwater resources and the increasing scarcity, cost and political controversy associated with securing new sources of supply has encouraged efforts to find new ways of meeting current water requirements. The sustainable reuse of greywater is a viable option that may help to lighten some of this pressure and could be a key strategy that reduces water demand and increases its availability for primary users, such as domestic and animal life or agriculture.
A re-usable resource
Greywater, although the definition varies in different parts of the world, generally refers to water from all non-toilet household activities and includes baths, showers, washbasins and clothes washing machines or the laundry. Toilet water and water from kitchen sinks is considered black water, as this contains elevated levels of pathogens, nitrogen and other elements that require treatment at a sewage treatment works. Greywater constitutes the largest volume of water wasted through general consumption. An average household (family of four) will consume between 200 and 300 ℓ of potentially reusable water on a daily basis. Between 50 and 80% of which is wasted could be reusable greywater. By appropriately matching water quality to water need, the reuse of greywater can replace the use of potable water in non-potable applications like toilet flushing and landscaping. This could offer significant savings in water usage as well as supplement basic water supplies during times of restriction or scarcity. The reuse of greywater will also reduce the requirement for wastewater treatment by reducing the hydraulic flow received by the utilities. This will become increasingly important as wastewater generation from cities is expected to reach unprecedented volumes in the coming decade due to rapid urbanisation in cities across Africa. Disposal of wastewater is a serious problem in African cities as many cities lack the infrastructure or technology to effectively accommodate and treat wastewater or have functional water service utilities (or legislative frameworks) to assist in effective water management.
For many rural communities, greywater can provide valuable sustenance for agricultural crops as well as meet a wide range of other social and economic needs. It utilises a valuable on-site resource and reclaims otherwise wasted nutrients. Many lower income or rural communities live without access to a household water connection. In these communities, women and children often have to walk long distances or wait in line in order to access water, which then needs to be carried home. In these households, reusing water in the home and for household gardens/horticulture is critical as it reduces the reliance on freshwater supplies while contributing to food production, thereby improving rural livelihoods. In developed countries, the use of greywater has already reduced freshwater demand, strain on wastewater treatment plants and energy consumption. Aquifer recharge is improved in some areas due to increased infiltration flows and plant growth is supplemented from the additional nutrients present in the outflow water. Water savings are consequently increased and expenses reduced, as consumption of municipality controlled freshwater supplies in these urban and peri-urban areas are decreased.
The use of greywater needs to be carefully controlled and monitored, as the inherent nature of the outflow water will vary according to the source. The temperature and nutrient value contained in greywater provide the perfect environment for anaerobic bacteria to breed and produce by-products such as methane and hydrogen sulphide. Furthermore, the original constituents used – such as phosphates or boron in washing powder, which may be toxic to plants at high concentrations, or salts, which may impact on the saline levels of the soil – may cause soil contamination or, worse, leach into the groundwater. Unchecked, the use of greywater has the potential to cause harm to both human health and the environment. The receiving environment cannot neutralise and assimilate all greywater pollutants, so the responsibility lies with user to ensure that the quality and quantity of their greywater meets the appropriate requirements. Good education, management and monitoring policies will be required to ensure effective community greywater usage; however, the benefits will still greatly outweigh the input required.
However, if used in an environmentally friendly manner, the risks associated with the reuse of greywater to the environment are low. The topsoil is the most biological active layer of the soil profile and if the system is not overloaded, it can efficiently remove excess nutrients from the greywater, including organic material, nutrients, salt and sediment. This preserves natural groundwater sources and may result in additional recharge of groundwater sources in areas where the water table is sufficiently high. Greywater therefore offers a variety of opportunities as well as challenges. Greywater technologies do exist, but the availability, use and policies for such technology vary widely around the world. Many regions lack clear regulations or standards regarding greywater capture and reuse. Rural communities certainly may not have access to adequate knowledge, infrastructure or funds to assess and treat greywater before reuse, should this be required. Therefore the implementation of greywater reuse benefits from a participatory approach and an understanding of the inherent nature of the source of the water, as well as the direct needs and concerns of the user or surrounding community. At a smaller, more local scale, the benefits cannot be underestimated. These include reduced reliance on potable freshwater for non-potable related activities, supplementation of basic water supplies in times when demand outstrips supply or during times of restriction or scarcity, reduced loads on wastewater disposal systems and reductions in costs.
Small demonstration projects and new, more flexible, greywater policies have demonstrated the successful use and benefits of greywater at multiple scales