Sewage sludge is a useful raw material, not waste

Sludge is always produced if waste water treatment is performed using activated sludge or primary sedimentation tanks or septic tanks. Although sludge contains toxic pollutants (such as heavy metals and micropollutants) it also contains a big number of organic and nutrient substances such as nitrogen and phosphorus. Annually more than 10kg of sludge (dry solid) is produced per one person.

Sludge is organic matter derived from photoautotrophic activity. Therefore, as a final purpose, the most reasonable idea is to return this product back to nature instead of its incineration and land burial. However, all ideas to use sludge as organic fertilizer in natural ecosystems (forests, agriculture) fail because of the necessity to remove toxic substances from sludge.

We have studied most widespread and innovative methods of sludge disposal for Moscow city. Testing of all technologies was carried out in huge industrial companies. We suggest that sludge should be divided into several categories and used depending on the pollution substance indicators.

The first method to use less-contaminated sludge is to use it as a raw material to produce fertilizers. Clean biomass produced in agricultural fields can also be recycled into biofuel. 

The second method is composting which is common, for example, in the USA. This method allows to obtain high quality organic fertilizer without organic pollutants and pathogens which are removed during composting process.

In case of sludge contamination, we suggest its dilution (by adding peat, sand or subsoil) to obtain pollutant concentration at TLV level in soils.

Ready-made soils are already used for Moscow greening and in hothouses.

Besides, a new innovative product has been made – organic pods for corn seed planting. This method permits to use the most contaminated sludge, converting contaminants into micro-additives which are essential for plants. Under this single-point method of sludge application contamination of agricultural fields is impossible. This technology is related to precision agriculture 

One more method to apply highly contaminated sludge is to produce building materials. Our specialists have a successful experience of collaboration with building materials plants in the Moscow region. For instance, sludge can be added to produce cement (dry solid up to 50%) and granular foam glass (dry solid up to 20%).