What is Blackwater?

Experts consider the wastewater from toilets to be blackwater. Blackwater contains urine and feces (excreta) which is combined with flush water and toilet paper and fed into the sewer system. After flushing the blackwater into the municipal sewer system, it is transported to a facility in which treatment and recovery takes place. The daily amount of blackwater produced depends on your type of toilet. Although a person generates only 1.5 liters of waste on average per day, this amount increases to 25 to 50 liters per day with the additional quantity of flush water which varies dependent on the flushing system. 

Properties of Blackwater

Blackwater, unlike other wastewater streams, consists of a large proportion of organic matter, and, due to high phosphate and nitrogen concentrations, is particularly rich in nutrients. However, studies show that the concentration of pathogens and micro-pollutants such as drug residues is higher in blackwater than that of other wastewater streams. A return of the water to the countryside - especially when mixed with other wastewater streams, such as greywater and rainwater - therefore requires an energy-intensive cleaning process.

But it could be done differently: A separation of the blackwater from the other wastewater streams allows for the use of alternative treatment and recovery processes. The chemical energy bound in the organic material can be utilized through anaerobic treatment. For example, the blackwater can be digested in a biogas plant, producing a source of renewable energy. Thus, the recycling of blackwater performs an ecological service and makes a contribution to the field of renewable energy. 

Blackwater in the HAMBURG WATER Cycle®

Conventional wastewater systems ensure that black- and grey- water be disposed of and treated. In certain areas, rainwater is also fed into wastewater streams. The HWC specifies the separation of the domestic wastewater flows, thus fundamentally changing wastewater management.

The separation of wastewater streams is desirable, particularly in regard to material and energy recovery from the blackwater. Blackwater which is less dilute becomes much more profitable for energy production. Therefore, the blackwater in HAMBURG WATER Cycle® is consistently separated from the greywater and the rainwater.

To further concentrate the blackwater, water-saving toilets are used in the HWC concept. There are different types of toilets that allow for the feeding of blackwater into the sewer system. The conventional disposal system provides for the use of a flush toilet. A compelling alternative is the vacuum toilet.This consumes only about one liter of water per flush, saving around five to nine liters per flush when compared with conventional flush toilets.

The concentrated blackwater is then combined with other biomass sources such as organic waste in an anaerobic digester. Biogas is then formed through the fermentation process, which is converted into electricity and heat through a combined heat and power (CHP) process. In the HWC, blackwater is considered more than just waste: through the use of a biogas plant, it is considered to be an essential resource of renewable energy.