The application of sulfate reducing bacteria (SRB) to treat municipal wastewater is seldom considered. For instance, due to low sludge yield it can reduce the amount of excess sludge produced significantly. Several studies, mainly at laboratory-scale, revealed that SRB can proliferate in artificial wastewater systems at temperatures of 20°C and lower. So far, the application of SRB in a domestic wastewater treatment plant has been limited. Therefore, this study evaluates the proliferation of SRB at pilot-scale in a moderate climate. This study revealed that SRB were present and active in the pilot fed with domestic wastewater at 13°C, and outcompete methanogens. Stable, smooth and well-settled granule formation occurred, which is beneficial for full-scale application. In the Netherlands the sulfate concentration is usually low (,500 mg/L), therefore the application of SRB seems challenging as sulfate is limiting. Additional measurements indicated the presence of other sulfur sources, therefore higher sulfur levels were available, which makes it possible to remove more than 75% of the chemical oxygen demand (excluding sulfide) based on SRB activity. The beneficial application of SRB to domestic wastewater treatment might therefore be valid for more locations than initially expected.

Current practice of wastewater treatment does not recover the full potential of energy present in wastewater. The potential of using anammox bacteria for autotrophic nitrogen removal combined with a desire for energy optimization brings new attention to the A-stage technology for organic carbon harvesting from municipal wastewater. The goal of this research was to investigate operational conditions of four full-scale A-stage processes and gain insight in the optimal conditions to harvest the maximum amount of organics present in sewage as excess sludge from the A stage. Large differences in removal efficiencies and design aspects were found between the four operational A-stage processes in the Netherlands. Biochemical oxygen demand (BOD) removal efficiencies vary between 40% and 80%, indicating that a good removal efficiency is possible, but that local conditions or design can be very influential. An optimal solid retention time (SRT) for maximal sludge production of 0.3 days was found; a longer SRT resulted in more mineralization of the chemical oxygen demand (COD). SRT control might be an important design aspect for the optimization of A-stage process. A short contact time with a minimum of 15 min and sufficient aeration were found to be optimal for soluble COD removal. Iron addition aided the removal of colloidal/suspended COD by coagulation/flocculation. Sludge flocs formed in the A-stage process are weak and sensitive to anaerobic conditions as well as shear due to, for example, pumping. Besides a good design of the A-stage itself, the further processing of the produced sludge also needs careful attention to optimize the sludge production and energy production.

Sulfate-reducing bacteria (SRB) can beneficially be applied to domestic wastewater treatment. In general, formed sulfide will stay in liquid phase, resulting in an elevated sulfide content, which might have inhibiting effects on the SRB. To study effects of environmental conditions on the SRB resistance against sulfide, two sequencing batch reactors fed with artificial domestic wastewater were operated at sulfate-reducing conditions. Required sulfide concentration within the reactor was achieved by adding 400 or 800 mg COD/L (acetate and propionate), the latter resulting in proportionally more sulfide production. Batch tests revealed that sulfide inhibited the rate of sulfate reduction by 50% at a concentration of 200 mg/L sulfide for biomass from the reactor fed with 400 mg COD/L. After adaptation to a feed of 800 mg COD/L, resulting in higher sulfide exposures, sulfide was less inhibitive to SRB. Complete COD removal was achieved in the reactor fed with 800 mg COD/L, and the SRB population changed from one (Desulfotalea arctica) to two (Desulfobacter postgatei and Desulfocapsa sulfexigens) dominant species. Results indicate that SRB are capable of adapting to higher sulfide exposure. Therefore, the SRB can also be applied to treat wastewater with higher COD levels, blackwater for instance.