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In most municipal wastewater treatment plants (MWWTPs) that employ activated sludge systems for nitrogen (N) removal, aeration accounts for approximately 50–60 % of all electricity consumption. Deammonifikation (DEA) is well-recognized as an energy–efficient technology although its mainstream implementation is still questionable. The aim of the presented work was to determine the operational window of various deammonifying sludges (S1–S7) in NRW from side of MWWTPs with respect to the operational factors temperature (8–50 °C), pHvalue (3.5–10.5), and COD/N ratio (0.5–6). Efficiencies up to 3 mg N L⁻¹h⁻¹were achievable even below 15 °C except for S6. All of the sludges except S6 achieved an elimination rate of more than 2.08–16 mg N L⁻¹ h⁻¹ in the main stream pH range (7–8). At a COD/N ratio > 1.5, the metabolism of DEA was disturbed. Although N/DN was suspected to have occurred at higher COD/N ratio, no increase in elimination rate was observed for most of the sludges. All the sludges fulfilled the minimum requirement of N-elimination rate (2.08 mg N L⁻¹h⁻¹ ), which leads to a comparable reactor volume to conventional WWTP. A large-scale implementation of a main stream DEA in full stream cannot yet be recommended on the basis of these results but semi-technical trials.
This study investigated the anaerobic digestion of an algal–bacterial biofilm grown in artificial wastewater in an Algal Turf Scrubber (ATS). The ATS system was located in a greenhouse (50°54′19ʺN, 6°24′55ʺE, Germany) and was exposed to seasonal conditions during the experiment period. The methane (CH4) potential of untreated algal–bacterial biofilm (UAB) and thermally pretreated biofilm (PAB) using different microbial inocula was determined by anaerobic batch fermentation. Methane productivity of UAB differed significantly between microbial inocula of digested wastepaper, a mixture of manure and maize silage, anaerobic sewage sludge, and percolated green waste. UAB using sewage sludge as inoculum showed the highest methane productivity. The share of methane in biogas was dependent on inoculum. Using PAB, a strong positive impact on methane productivity was identified for the digested wastepaper (116.4%) and a mixture of manure and maize silage (107.4%) inocula. By contrast, the methane yield was significantly reduced for the digested anaerobic sewage sludge (50.6%) and percolated green waste (43.5%) inocula. To further evaluate the potential of algal–bacterial biofilm for biogas production in wastewater treatment and biogas plants in a circular bioeconomy, scale-up calculations were conducted. It was found that a 0.116 km2 ATS would be required in an average municipal wastewater treatment plant which can be viewed as problematic in terms of space consumption. However, a substantial amount of energy surplus (4.7–12.5 MWh a−1) can be gained through the addition of algal–bacterial biomass to the anaerobic digester of a municipal wastewater treatment plant. Wastewater treatment and subsequent energy production through algae show dominancy over conventional technologies.
