A novel hybrid airlift bioreactor (HALBR) for simultaneous carbon and nitrogen removal from composting leachate was studied. In contrast to conventional airlift bioreactors, an anaerobic chamber was mounted at the bottom part to improve biodegradability of composting leachate and optimize overall COD removal. Desired aerobic and anoxic conditions provided by airlift configuration and oxygen concentration gradients within the biofilm increased the capability of system for TN removal through SND. Three independent variables, hydraulic retention time (HRT) (18–30 h), air flow rate (AFR) (1–2 L_air/min), and aerobic volume ratio (AVR) (0.22–0.26) were evaluated as operating parameters. The optimum conditions were an HRT of 28.3–30 h and AFR of 1.7–2 Lair/min, giving 3600 mg/L (90%) of COD and 598.4 mg/L (80%) of TN removal, respectively with an effluent turbidity less than 70 NTU. The outcomes demonstrated that this innovative single HALBR is a feasible and reliable technology for treatment of composting leachate.

Operational disturbances in aerobic granular sludge (AGS) systems can result in aerobic availability of readily biodegradable COD (rbCOD). Different from activated sludge, morphological consequences on the short and long term are not well described in literature. This study investigated the effect of incomplete anaerobic uptake of acetate on the morphological and process stability of AGS using a lab-scale reactor. A fraction of the total acetate load was dosed aerobically, which was increased stepwise while monitoring granular morphology. A good granular morphology and an SVI of 40 ml/g were obtained during initial enrichment and maintained for ≤20% aerobic acetate load dosed at 4 mg COD/g VSS/h. Biological phosphorus removal efficiency was initially unaffected, but the aerobic acetate dosage rate did decrease the aerobic phosphate uptake rate. This led to loss of phosphorus removal for >20% aerobic acetate load dosed at 8 mg COD/g VSS/h over the course of 12 days. Subsequently, significant outgrowth formed on the granular surfaces and developed over time into finger-like structures. Under these high aerobic acetate loads the SVI increased to 80 ml/g and resulted in significant biomass washout due to deteriorating settling properties of the sludge. The sludge settleability and biological phosphorus removal recovered 10 days after aerobic feeding of acetate was stopped. Aerobic presence of rbCOD can be tolerated if mostly anaerobic acetate uptake is maintained, thereby ensuring stable granular morphology and good settleability. The high enrichment of phosphate accumulating organisms in the granular sludge through bottom-feeding and selective wasting of flocs makes aerobic granular sludge resilient to morphological deterioration in aerobic presence of rbCOD.

In recent years, source-separated human urine has been highlighted as an effective resource for energy and nutrient recovery. However, even though several technologies exist for resource recovery, they have not been widely implemented. Among these technologies, bioelectrochemical systems (BESs) hold promise as technically and economically interesting alternatives for sustainable resource recovery from source-separated urine. Here, we review the resource recovery performance of BESs, including microbial fuel cells (MFCs) and microbial electrolysis cells (MECs), fed with source-separated urine over the past decade, and suggest an effective path forward toward their widespread implementation.

The feasibility of a continuous feed and intermittent discharge airlift bioreactor for simultaneous carbon and nitrogen removal from a low COD/N wastewater was evaluated. The effect of two independent variables, HRT (10–20 h) and NH₄ ⁺/(NH₄ ⁺+NO₃ ⁻) ratio (0.25–0.75), on the bioreactor performance was studied. The relatively high anaerobic to aerobic time ratio made an effective contribution to NH₄ ⁺, NO₃ ⁻, and TN removal. TN removal was enhanced with increase in HRT and decrease in NH₄ ⁺/NH₄ ⁺+NO₃ ⁻ and at the optimum condition, 616 mg/L (88%) and 213 mg/L (76%) of sCOD and TN were removed, respectively. The results suggested that the nitrogen removal process was based on a combination of anaerobic ammonium oxidation (Anammox), simultaneous nitrification-denitrification (SND), and presumable dissimilatory nitrate reduction to ammonium (DNRA) mechanisms.