Sustainable design of the water-energy-waste nexus in new settlements: the case of Curauma

Traditional urban waste water collecting and treatment systems generally fulfill the main purposes of such systems quite well, i.e. keeping living areas dry and removing of waste substances and pathogens from settlements. But... [ view full abstract ]

Traditional urban waste water collecting and treatment systems generally fulfill the main purposes of such systems quite well, i.e. keeping living areas dry and removing of waste substances and pathogens from settlements. But waste water treatment plants (WWTP) could be part of a decentralised energy system. Since regarding volume the most important solid by-product is sludge, which could be fermented to produce biogas. However, the overall energy efficiency is still rather low: WWTP, which are enabled to produce sludge, consume 10 kWh_el per person and year.

The aim of the presentation is to discuss a concept which combines separate waste water flow treatment systems with separate solid waste collecting systems to enhance the energy efficiency of WWTP but also to reduce the water and energy demand by households. The general idea of a separate flow treatment system is at first to split waste water flows according to their sources of waste water generation, their specific volumes and compounds to enhance the recycling of inherent energy and substances. The most simplified system parts grey water, e.g. waste water from showers, from black water, i.e. human excreta. Whereas grey water could be used as an additional heat source in buildings, black water would be transported to anaerobic digestion plants. 

To enhance the energy efficiency of WWTPs additionally organic waste shall be added. A pre-requisite for this is a collecting system of solid waste, which seperates household waste. 

However, a successful implementation of such systems depends crucially amongst others on climate conditions and the socio-cultural background. The presented discussion will reflect the situation in Curauma in Central Chile making use of the results of a process-based material flow approach, using data describing the situation in the mentioned neighbourhood. In such a system it is expected that WWTP could generate up to 25 to 30 kWh_el per person and year. The water demand could be reduced by about 30%; the demand for energy could cet. par. decline noteworthy. 

Combining smart waste water treatment systems with decentralized energy systems could improve energy efficiency of locally available energy sources considerably, reducing the water demand significantly which is of high relevance in particular in semi-arid regions, like Central Chile.