Sludge Composting: Q&A

Q1: Does sludge composting need additives?

A1: Yes. If the moisture content of the sludge is lower than 60% and the organic matter is greater than 70%, additives don’t have to be added. Additives are plant materials added in the composting process. They are characterized by low moisture content, loose and high organic matter. Additives play three roles in composting: regulating water content, regulating porosity, and supplementing organic matter.

Q2: Are there any standards for sludge composting?

A2: Yes. According to different needs and disposal ways, it is mainly divided into: Standards for Control of Pollutants in Agricultural Sludge (GB4284-2018), sludge disposal in urban sewage treatment plants - sludge for landscaping, sludge for land improvement and so on.

Q3: How much does sludge composting cost to operate?

A3: About $22~$30. The main operating costs of sludge composting include: electricity, additives, labor costs and so on. The current processing technology is $22~$30, of which the cost of additives can account for 60%, labor and electricity account for 40%.

Q4: Can sludge composting remove heavy metals?

A4: No. For municipal sewage, sludge heavy metal is generally not exceeding the standard. But due to the release of supervision, other heavy metal sludge may enter the soil. In short, composting does not remove heavy metals.

Q5: What is the fermentation temperature of sludge composting?

A5: The initial temperature is indoor or outdoor temperature, above 50℃ into the high temperature fermentation stage. The higher the temperature, the fewer the species of living bacteria and the lower the degradation efficiency of organic matter. High temperature plays the role of sterilization, harmlessness and material drying in the process of fermentation.

Q6: What is primary fermentation and secondary fermentation?

A6: Primary fermentation mainly refers to high temperature fermentation, that is, heating to high temperature to lower the initial temperature stage. Secondary fermentation is when most of the organic matter is degraded, not enough support to maintain high temperature, but slow degradation, gradual heat dissipation, still can maintain the temperature of 40℃, also known as secondary aging.

Q7: Why aging?

A7: Aging is an important and slow process for humification of organic matter. High temperature fermentation can degrade organic matter quickly and easily, while aging can degrade organic matter slowly and humify it.