Many municipal wastewater treatment plants (WWTPs) or water and resource recovery facilities (WRRFs) are striving to achieve energy self-sufficiency in their process operations, while simultaneously complying with permit requirements. Currently, less than 10% of U.S. WWTPs or WRRFs produce energy for beneficial use and only a handful of these plants are actually energy self-sufficient. This research seeks to assess the current state-of-knowledge on energy-positive WWTPs or WRRFs, based on the treatment train classification named as “Basic”, “Moderate”, and “Advanced”. A simple quantitative mass-balance model (SQMM) is developed to evaluate the treatment train or technology classification in terms of removal and recovery of carbon-nutrient-energy components of municipal wastewater(s). The goal of this research is to identify potential challenges in the selection and implementation of resource and energy recovery process configurations and, propose practically feasible, energy-positive WWTP process configurations. Currently, energy recovery through biogas production, and aeration energy optimization are the two main approaches to achieve energy self-sufficiency. The main alternative strategy to enhance energy recovery in the near future is by co-digestion of wastewater biosolids and locally available biodegradable wastes. A hypothetical (but practically feasible) WWTP or WRRF configuration proposed in this work represents an alternative energy self-sufficient wastewater process train for future designs. A detailed quantitative analysis will be developed to recommend the ways in which WTTPs or WRRFs could become energy-positive and achieve maximum resource recovery.

Current wastewater treatment processes such as activated sludge process and other aeration technologies are resource-consuming and are unsustainable. Novel and integrated processes are crucial to the development of sustainable wastewater treatment systems. In this context, anaerobic treatment technologies provide numerous opportunities for minimization of energy and resource consumption and maximization of beneficial products. Further, integration of anaerobic digestion augmented by co-digestion, fermentation, dark fermentation or photo-fermentation and other bioelectrochemical systems may result in resource-efficient waste management and environmental protection. This mini-review discusses various possibilities and highlights recent developments of integrated aerobic and anaerobic technologies with bioelectrochemical systems for sustainable wastewater treatment.

This research investigates a novel platform for an energy-yielding wastewater treatment and desalination scheme in which the organic matter present in wastewater is purposely fed to the exoelectrogenic bacteria to produce bioelectricity in a three-compartment bioelectrochemical system called photosynthetic microbial desalination cell (PMDC). The role of an inorganic carbon source in the microalgae biocathode was studied. Addition of sodium bicarbonate (NaHCO3) increased power production, microalgae growth and desalination rate. A power density of 660 mW/m3 was measured which is about 7.5 times higher than the PMDCs without NaHCO3. Desalination rate was more than 40% after 72 h. Overall, the process could be energy-positive while producing 4.21 kWh per m3 of wastewater treated including desalination energy savings and microalgae biomass energy potential.

The synergistic effect of microwave and ultrasound irradiations was evaluated for biodiesel production from microalgae biomass (Nannochloropsis sp.) as raw material. A response surface methodology technique based on central composite design was used to understand the process parametric interdependence and optimize the process reaction variables. Reaction kinetics of algal fatty acid methyl ester (FAME) production was also studied. The optimum reaction conditions were determined as wet algal biomass to methanol ratio of 20 g to 30 mL, 1 wt% catalyst concentration, and 7-minute reaction time at 140 W of microwave power and 140 W of ultrasound power. The estimated activation energy was 17,298 J/mol−1 K−1 for a first-order reaction kinetics. This study revealed that microwave energy dissipation at a low rate of 140 W combined with 140 W of ultrasound intensity is adequate to produce FAMEs at a maximum yield of 48.2%. Results from this optimization study suggest that a more detailed and mechanistic energy optimization study is critical to increase the FAME yield and maximize energy benefits.