• Energy Research

The article provides comparison of operation of digesters for 2014, installed in wastewater treatment plants (WWTP) of two Lithuanian cities Kaunas and Klaipėda. It was established that the temperature and decomposition degree of organic materials had impact on biogas discharge in digesters of both wastewater treatment plants. Increase of these technological parameters resulted in increase of biogas output. Actual output of biogas of Kaunas wastewater treatment plant digester was by 5.8 % less than theoretical output, in Klaipėda WWTP anaerobic reactor – by 4.2 %. After comparison of biogas discharge generated from 1 m3 of sludge in Kaunas and Klaipėda WWTPs it was established that the efficiency of Klaipėda WWTP digester exceeded the efficiency of Kaunas WWTP reactor by 7 %.

Management of waste water sludge is one of the most topical environmental problems that is being gradually solved in Lithuanian waste water treatment plants. Anaerobic sludge digestion is an essential part of sludge treatment. Digestion process not only mineralizes organic pollutants and reduces amount of sludge, but also produces biogas which can be used for energy needs. Different technological and hydraulic factors affect work efficiency of digester. This article analyses the effect of temperature, amount and composition of sludge as well as the process of stirring sludge on gas discharge in Kaunas WWTP digester. It has been determined that degradation degree of organic material affects production of biogas. Sludge digestion process is performed in a narrow temperature interval and for this reason no temperature effect has been observed on the machinery. By stirring sludge effectively a better biogas output can be obtained.

The presence of potentially toxic elements (PTEs) in soils can upset the natural balance and increase the risk of PTE incorporation into the food chain. The use of composite biochar with municipal sewage sludge compost (MSSC/C) can be an effective way of both managing waste, such as sewage sludge, and providing an effective additive-supporting phytostabilization processes. The effectiveness of D. glomerata and MSSC/C in the technique of assisted phytostabilization of industrially contaminated soils was determined under the pot experiment conditions. The PTE contents in D. glomerata and the soil were determined using the spectrophotometric method. The addition of MSSC/C to PTE-contaminated soil contributed to an 18% increase in plant biomass and increased the soil pH by 1.67 units, with the PTE concentration being higher in the roots than in the above-ground parts of D. glomerata. The MSSC/C addition had the strongest effect on the reduction in Cd, Cr, and Ni contents in the soil following the completion of the experiment. The current study confirmed the effectiveness of MSSC/C in aiding the phytostabilization processes in PTE-contaminated soils.