Consideration on carbon emission and carbon emission reduction of sewage treatment system

Second, improve the efficiency of energy recovery in sewage

There are a lot of organic matter in the effluent of the municipal sewage treatment plant, which needs to be removed in order to make the effluent meet the discharge standard. In the traditional activated sludge process, these organic matter are converted to CO2 through an aerobic process. However, these organics actually contain a lot of chemical energy, which is better converted into biogas (such as CH4 or H2) for use than being removed by "energy dissipation". CH4 is a clean energy source with a high heat of combustion, with a calorific value of 8.4×104kJ/kg, which can provide both electrical energy and heat energy during combustion. At present, the influent organic matter concentration of the sewage treatment plant is 400mgCOD/L, and the initial sludge and the remaining sludge are anaerobic digested to produce CH4 and implement cogeneration, and the energy output is much higher than the energy input of the anaerobic digestion tank.

The process of anaerobic digestion to recover biogas from organic matter has been widely used in Europe and the United States. The Strass sewage treatment plant in Austria produces CH4 anaerobic by using the residual sludge, and the operation energy balance rate can reach 108%, that is, the sewage treatment plant can meet its entire energy consumption only by recycling the organic energy in the residual sludge. Although the core technology of sludge anaerobic digestion energy recovery to produce CH4 has been developed and mature, it is only economically feasible to install in large and medium-sized sewage treatment plants, and less than 5% of urban sewage treatment plants in China currently use sludge anaerobic digestion systems.

Third, find other external renewable energy sources

Sewage treatment plants require a certain amount of land, which can be filled with solar panels or with external wind power. For example, if photovoltaic panels are spread over the entire sewage treatment plant, nearly 10% of the operating energy consumption can be covered.

05 Outlook

Sewage is rich in fresh water, energy and nutrients, rather than "waste". With the advancement of technology, the idea of achieving carbon neutrality in wastewater treatment in the future, or even becoming an "energy factory" is not a dream.