According to UNESCO, poor wastewater management, or lack of it, means that only 20% of global wastewater receives proper treatment. With wastewater directly impacting biodiversity of aquatic ecosystems, disrupting their integrity and services humans rely on for health and economic development, UN-Water has called for wastewater to be considered as part of an integrated, full-lifecycle, ecosystem-based management system that operates across transboundary and supports sustainable development.
With many countries facing high capital expenditure costs in developing or expanding wastewater treatment systems to increase the percentage of wastewater being treated, less expensive decentralized systems can supplement or replace traditional wastewater treatment plants (WWTPs).
What is wastewater?
Wastewater is a combination of one or more of:
- Domestic effluent consisting of blackwater (human waste) and greywater (kitchen, bathing wastewater),
- Water from commercial establishments and institutions including hospitals,
- Industrial effluent, stormwater and other urban runoff,
- Agricultural, horticultural dissolved or suspended matter.
Wastewater contains plant nutrients (nitrogen, phosphorous, potassium), pathogenic micro-organisms (viruses, bacteria, protozoa), heavy metals (cadmium, chromium, copper, mercury, nickel, lead, zinc), organic and inorganic pollutants and micro-pollutants (medicines, cosmetics, cleaning agents).
Hamburg’s decentralized wastewater solution
In Germany, Hamburg Wasser has developed the Hamburg Water Cycle (HWC) – an innovative decentralized wastewater solution of the future based on source separation where waste is turned into energy, greywater from washing is used for gardening while a separate stormwater system allows rainwater to replenish ground and surface water.
To test the HWC concept, Hamburg Wasser has revitalised the former Lettow-Vorbeck military barracks into a new urban settlement called ‘Jenfelder Au’. The Jenfelder Au Settlement covers over 35 ha with 770 accommodation units. The land allocation is: Habitation (60%), trade and commerce (20%) and green (20%) with construction concluding in 2016.
To ensure waste remains concentrated, the Jenfelder Au settlement will implement a vacuum toilet and sewage system that reduces water use in flushing toilets by approximately 80% – as suction, rather than water, will transport waste into the sewage system. Specifically, the new vacuum system will use 0.5 – 1 litre of water per person per day flushing compared to a conventional toilet’s 6-8 litres per person per day. Therefore, waste (organic matter, nutrients) will remain concentrated enabling it to be extracted for anaerobic treatment before being used for energy production on-site (with zero carbon emissions).
Economic and environmental benefits
There are multiple economic and environmental benefits of utilising decentralized solutions to supplement or replace WWTPs including:
Lower treatment costs: Less wastewater entering wastewater treatment plants lowers treatment costs (chemical and energy).
Lower operational and maintenance costs: More higher-concentrated wastewater improves the operational efficiency of WWTPs, reducing operational and maintenance costs.
Reduced capital expenditure: Lower volumes entering WWTPs mean utilities can avoid, downsize or postpone expensive wastewater treatment projects and increase the lifespan of existing WWTPs.
Climate resilient: Lower volumes of stormwater entering WWTPs means cities have adequate capacity to handle higher wet-weather volumes with climate change, ensuring WWTPs are ‘right-sized’.
Reduced compliance costs: Decentralized systems can help utilities reduce, defer and avoid capital costs of new, expanded WWTPs necessary to meet regulatory compliance (e.g. Clean Water Act, EU Urban Waste Water Directive).
Less pollution: In combined systems, decentralized systems can reduce the volume of stormwater entering the sewage system during heavy storm events reducing combined system overflows.
To increase the amount of wastewater being treated less expensively decentralized systems can supplement or replace traditional WWTPs, leading to numerous economic and environmental benefits.
*Robert C. Brears is the author of Urban Water Security (Wiley). Urban Water Security argues that, with climate change and rapid urbanization, cities need to transition from supply-side to demand-side management to achieve urban water security.