Smart sludge management solution for small-scale plants piloted at Türi and Oisu WWTP
Many good solutions for waste activated sludge management exist around the Baltic Sea Region, but most of them are not applicable for small wastewater treatment plants. A pilot investment was done in Türi and Oisu wastewater treatment plants (Estonia) in order to show a good example of efficient sludge treatment for small-scale plants by applying the technology of sludge humification beds. This technology allows treating sludge in a natural way without using any complicated mechanical facilities or chemicals, simultaneously ensuring low constructional and operational costs and low environmental impact.
Sludge humification is one of the solutions that provide an option for the phosphorus and nitrogen reuse: it is applicable on the small scale, it helps with decreasing and eliminating harmful substances and organisms from the sludge, and it allows using the treated sludge as a fertilizer.
Considering that sludge management in humification beds is a long-term process lasting at least three vegetation periods, the time- and site-based planning based on previous studies is an essential part of the piloting process. The humification beds in Türi and Oisu were constructed next to the wastewater treatment plants and they have the same working principle, while their structure is a bit different in order to determine the most feasible practice.
In Oisu, the beds were equipped with a leachate pumping system to lessen the amount of water in the humification beds during dewatering and plant growth period. In Türi, the excess water is not pumped away, as mechanical thickening is applied beforehand. The humification beds in both WWTPs are sowed with plants, which helps with the degradation of organic material, including refractory compounds, while also provides the ability to absorb the residues of toxic substances like heavy metals from the sludge. In order to extract the toxic substances absorbed in the plants, mowing or reaping can be used.
Inefficient sludge treatment in WWTP may lead to increased loads of hazardous substances to the Baltic Sea, however, efficient sludge treatment is challenging for small-scale WWTPs. Sludge humification bed is a technology feasible for small WWTP, but is underestimated in cold climate. Smart operation of the humification and degradation processes can convert the sludge into a quality product that can be applied in agriculture, greenery and recultivation.