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A study was undertaken to examine the feasibility of biologically treating a combined waste stream of landfill leachate and municipal sewage. The ratio of sewage to leachate was 9 to 1 by volume. The combined waste had an average BOD5 430 mg/l, COD 1090 mg/l, and TKN 133 mg/l (80% of which was in the form of ammonia). A laboratory-scale sequencing batch activated sludge reactor was used to carry comparative performance evaluations of biological treatment, including nitrification and denitrification. The SBR reactor was operating in daily time cycles employing the following sequential operation phases: filling phase, anoxic phase, aeration reaction phase, settling phase, and drain phase. In particular, the anoxic and aeration periods were tailored in order to develop conditions conducive to desired nitrification and denitrification. During the reaction period, the process was operated under an extended aeration mode with the MLSS concentration being around 3500 mg/l. The results indicated that successful biotreatment of combined leachate and sewage was possible, with the treated effluent being low in BOD5 and COD. The system was capable of BOD5 removal efficiencies exceeding 95%. Furthermore, nitrate removal during the anoxic phase was approximately 99% due to denitrification. However, the overall nitrogen removal during a full cycle was about 50%. The inclusion of an anoxic period right after the aeration phase enhanced the nitrogen removal efficiency, yet this phase required the addition of an external carbon source to the reactor due to the low concentration of biodegradable carbon, and at the same time the process became less efficient in BOD removal.

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Wastewater treatment, as a crucial component of the urban water environment, consists of several energy-consumptive stages, therefore efficiency and energy savings measures are essential to maintain them as environmentally sustainable and economically viable. Operational and technical data from WWTPs in Greece have been collected as well as a sample from 61 facilities with key energy profile components. Energy consumption was assessed by specific key performance indicators (KPIs); specific energy consumption expressed per population equivalent (from 3 to 150 kWh/PE), per cubic meter treated (from 0.2 to 2.0 kWh/m3) and per unit of organic load removed (from 0.03 to 7.13 kWh/CODremoved).

Membrane fouling still remains a drawback for membrane bioreactors; there is nevertheless a natural promising solution which is the growth of filamentous microorganisms in moderate concentrations. In this project, an innovative 25 L membrane bioreactor is used, consisting of two aerated tanks and a membrane tank. The first tank is supplied with high Food/Microorganism (F/M) loading and the second tank with very low loading. The aerated tanks were constantly provided with dissolved oxygen (DO) 2.5 ± 0.5 mg/L. Finally, it is concluded that the imposed aeration conditions contribute to the growth and control of filaments in moderate concentrations having a filamentous index = 2 and therefore reducing membrane fouling for more than 1.5 months, maintaining the trans-membrane pressure at 1.4 ± 0.11 kPa.