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The application of anaerobic digestion technology is growing worldwide because of its economic and environmental benefits. As a consequence, a number of studies and research activities dealing with the determination of the biogas potential of solid organic substrates have been carrying out in the recent years. Therefore, it is of particular importance to define a protocol for the determination of the ultimate methane potential for a given solid substrates. In fact, this parameter determines, to a certain extent, both design and economic details of a biogas plant. Furthermore, the definition of common units to be used in anaerobic assays is increasingly requested from the scientific and engineering community. This paper presents some guidelines for biomethane potential assays prepared by the Task Group for the Anaerobic Biodegradation, Activity and Inhibition Assays of the Anaerobic Digestion Specialist Group of the International Water Association. This is the first step for the definition of a standard protocol.

Postaeration, where digested sludge is introduced into aerobic conditions, is a technology that could improve the quality of sludge and sludge liquor in many ways. Although it is a fairly simple process, only few data about the effect of postaeration have been published. In this study, batch experiments have been performed first, indicating that postaeration affects the total ammonia nitrogen (TAN) and sludge dewaterability. In the removal of TAN, both stripping and biological oxidation can play an important role depending on specific condition. Then the postaeration was investigated in a semicontinuous batch reactor. In addition, the effect of postaeration on the concentration of selected micropollutants such as pharmaceuticals, EOX and AOX was studied. The hydraulic retention time (HRT) of 8, 6, 4 and 2 days and different aeration intensities were tested. The TAN removal efficiency achieved was about 40–60%, sludge dewaterability expressed by sludge cake total solids (TS) concentration after dewatering improved relatively by 5–30%. In addition, TS degradation is also taking place and therefore the reduction of the amount of final sludge to be disposed could be even higher. The biggest changes in observed parameters were recorded at the longest HRT.

Abstract Energy consumption of municipal wastewater treatment plants can be reduced by the anaerobic pre-treatment of the main wastewater stream. After this pre-treatment, nitrogen can potentially be removed by partial nitritation and anammox (PN/A). Currently, the application of PN/A is limited to nitrogen-rich streams (>500 mg L−1) and temperatures 25–35 °C. But, anaerobically pretreated municipal wastewater is characterized by much lower nitrogen concentrations (20–100 mg L−1) and lower temperatures (10–25 °C). We operated PN/A under similar conditions: total ammonium nitrogen concentration 50 mg L−1 and lab temperature (22 °C). PN/A was operated for 342 days in a 4 L moving bed biofilm reactor (MBBR). At 0.4 mg O2 L−1, nitrogen removal rate 33 g N m−3 day−1 and 80 % total nitrogen removal efficiency was achieved. The capacity of the reactor was limited by low AOB activity. We observed significant anammox activity (40 g N m−3 day−1) even at 12 °C, improving the applicability of PN/A for municipal wastewater treatment.

Anaerobic digestion is the only energy-positive technology widely used in wastewater treatment. Full-scale data prove that the anaerobic digestion of sewage sludge can produce biogas that covers a substantial amount of the energy consumption of a wastewater treatment plant (WWTP). In this paper, we discuss possibilities for improving the digestion efficiency and biogas production from sewage sludge. Typical specific energy consumptions of municipal WWTPs per population equivalent are compared with the potential specific production of biogas to find the required/optimal digestion efficiency. Examples of technological measures to achieve such efficiency are presented. Our findings show that even a municipal WWTP with secondary biological treatment located in a moderate climate can come close to energy self-sufficiency. However, they also show that such self-sufficiency is dependent on: (i) the strict optimization of the total energy consumption of the plant, and (ii) an increase in the specific biogas production from sewage sludge to values around 600 L per kg of supplied volatile solids.

The anaerobic digestion of primary and waste activated sludge generates biogas that can be converted into energy to power the operation of a sewage wastewater treatment plant (WWTP). But can the biogas generated by anaerobic sludge digestion ever completely satisfy the electricity requirements of a WWTP with ‘standard’ energy consumption (i.e. industrial pollution not treated, no external organic substrate added)? With this question in mind, we optimized biogas production at Prague's Central Wastewater Treatment Plant in the following ways: enhanced primary sludge separation; thickened waste activated sludge; implemented a lysate centrifuge; increased operational temperature; improved digester mixing. With these optimizations, biogas production increased significantly to 12.5 m3 per population equivalent per year. In turn, this led to an equally significant increase in specific energy production from approximately 15 to 23.5 kWh per population equivalent per year. We compared these full-scale results with those obtained from WWTPs that are already energy self-sufficient, but have exceptionally low energy consumption. Both our results and our analysis suggest that, with the correct optimization of anaerobic digestion technology, even WWTPs with ‘standard’ energy consumption can either attain or come close to attaining energy self-sufficiency.

The paper reviews results and experience of microaerobic experiments at both high and low sulphide concentrations and evaluates advantages and drawbacks of the anaerobic digestion of sludge in microaerobic conditions as regards biogas quality, digested sludge quality, organic pollutants biodegradability and methanogenic activity of biomass. The innovative microaerobic modification of the anaerobic sludge digestion technology was studied in both laboratory and full scale. Microaerobic conditions are obtained by dosing of a limited amount of the air into the liquid phase of the anaerobic digester. It was shown that anaerobic bacteria including methanogens can be active also in such system. In a mixed culture, even strict anaerobes can survive without inhibition, if the facultative microorganisms are able to consume the present oxygen quickly and fully. Until now, the microaerobic conditions were predominantly used for hydrogen sulphide removal from biogas. In the paper the role of the surplus oxygen was studied also at low sulphide concentration, when the oxygen is consumed in high extent for other processes beside sulphide oxidation.

Biogas, digested sludge and sludge liquor are the main products of anaerobic sludge digestion. Each of the products is influenced significantly by specific conditions of the digestion process. Therefore, any upgrade of the digestion technology must be considered with regard to quality changes in all products. Microaeration is one of the methods used for the improvement of biogas quality. Recently, microaeration has been proved to be a relatively simple and highly efficient biological method of sulfide removal in the anaerobic digestion of biosolids, but little attention has been paid to comparing the quality of digested sludge and sludge liquor in the anaerobic and microaerobic digestion and that is why this paper primarily deals with this area of research. The results of the long-term monitoring of digested sludge quality and sludge liquor quality in the anaerobic and microaerobic digesters suggest that products of both technologies are comparable. However, there are several parameters in which the ‘microaerobic’ products have a significantly better quality such as: sulfide (68% lower) and soluble chemical oxygen demand (COD) (33% lower) concentrations in the sludge liquor and the lower foaming potential of the digested sludge.

The treatment of solid wastes containing slowly biodegradable compounds or high level of sulphur compounds was carried out. In both cases the application of microaerobic conditions (that means controlled dosing of small amount of air or oxygen into digester) was an efficient tool to increase the biodegradability of treated material and/or to increase the activity of methanogenic bacteria by removal of their inhibitor.

Microaerobic alternative of anaerobic digestion offers many advantages especially when sulfide concentration in the digester is high. For better understanding of the microaerobic technology more detailed characterization of biomass activity is needed. Two equal digesters were operated under the same condition except of microaeration in one of them. During long term operation of anaerobic and microaerobic digesters the sludge quality and the biomass activity was monitored. The activity of sulfide oxidizing bacteria of microaerobic biomass was significantly higher in comparison with anaerobic biomass. The activity of sulfate reducing bacteria was comparable. The activity of methanogenic bacteria activity depended on sulfide concentration more than on microaeration. The extent of foaming problems was lower in the microaerobic than in the anaerobic digester.

Nitrogen removal from wastewater with high nitrogen concentration and low COD/N ratio via nitrite is advantageous. The specific character of the sludge liquor enables the application of such a method. The factors affecting process efficiency were studied. From the factors followed pH, NH4+/NH3 and NO2-/HNO2 concentration and distribution seem to be most important, using sequencing batch reactor technology and treating wastewater with high NH4+ concentration (above 1g/l). The efficient oxidation of N-NH4+ to nitrite was achieved at a minimal nitrate production. Primary sludge was used as an internal source of substrate for the denitritation because of the organic substrate deficiency of the sludge liquor. The denitritation can be controlled by dosing of the primary sludge and can be complete. There are two operational alternatives of sludge liquor pretreatment: without pH control - lower operational costs and N-removal up to 65% and with pH control - higher operational costs and N-removal close to complete.