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Low intensity surplus activated sludge pretreatment before anaerobic digestion

Suschka J., Grübel K.

Archives of Environmental Protection

2017

Vol. 43, no. 4

50--57

Sewage sludge (municipal, or industrial) treatment is still a problem in so far that it is not satisfactorily resolved in terms of cost and final disposal. Two common forms of sludge disposal are possible; the first being direct disposal on land (including agriculture) and the second being incineration (ash production), although neither of these methods are universally applied. Simplifying the issue, direct sludge disposal on land is seldom applied for sanitary and environmental reasons, while incineration is not popular for financial (high costs) reasons. Very often medium and large wastewater treatment plants apply anaerobic digestion for sludge hygiene principles, reducing the amount to be disposed and for biogas (energy) production. With the progress in sewage biological treatment aiming at nutrient removal, primary sludge has been omitted in the working processes and only surplus activated sludge requires handling. Anaerobic digestion of waste activated sludge (WAS) is more difficult due to the presence of microorganisms, the decomposition of which requires a relatively long time for hydrolysis. In order to upgrade the hydrolysis effects, several different pre-treatment processes have already been developed and introduced. The additional pre-treatment processes applied are aimed at residual sludge bulk mass minimization, shortening of the anaerobic digestion process or higher biogas production, and therefore require additional energy. The water-energy-waste Nexus (treads of) of the benefits and operational difficulties, including energy costs are discussed in this paper. The intensity of pre-treatment processes to upgrade the microorganism’s hydrolysis has crucial implications. Here a low intensity pre-treatment process, alkalisation and hydrodynamic disintegration - hybrid process - were presented in order to achieve sufficient effects of WAS anaerobic digestion. A sludge digestion efficiency increase expressed as 45% biogas additional production and 52% of the total or volatile solids reduction has been confirmed.

Energy and sustainability of operation of a wastewater treatment plant

Bodík I., Kubaská M.

Environment Protection Engineering

2013

Vol. 39, nr 2

15--24

The study summarises the energy consumption data obtained from the Slovak wastewater treatment plants. Overall, 51 large WWTPs using mesophilic anaerobic sludge digestion and biogas utilisation (the total capacity of 2.5 mil. p.e.) and 17 small rural WWTPs (the total capacity 15 000 p.e.) were compared in many technological and energy parameters. The average energy consumption in large WWTPs in Slovakia is 0.485 kWh/m3 and 0.915 kWh/m3 in small rural plants. The average energy demand related to BOD5 load represents the value of 2.27 kWh/kg BOD5, in Slovak plants. The specific energy production is relatively low - in average 1.2 kWh el /m3 of produced biogas and 0.1 kWh el /m 3 of treated wastewater, respectively. The average energy autarky in Slovak plants is 25.2%. Some plants have high energy autarky (>65%), despite no external biowastes being dosed to these during operation.