Energy-Positive, Carbon-Negative Wastewater Recycling & Resource Recovery

Summary:

UCLA Researchers in the Department of Civil and Environmental Engineering have developed a system for recycling wastewater that is net energy-positive and carbon-negative while generating pipeline grade natural gas and both liquid and solid fertilizer products.

Background:

Biological nutrient removal (BNR) is an important component of modern wastewater treatment, which is responsible for removing nutrients (nitrogen, phosphorus) from wastewaters in conjunction with biological removal of carbonaceous waste. If left untreated, nutrient-containing wastewater discharges cause algae blooms and eutrophication. The process is expensive due to the addition of anoxic and anaerobic bacterial reactors that work in-line with aerobic bacterial reactors and, in addition, the process results in the release of nitrous oxide, which has a greenhouse gas equivalent impact 298 times more intense than CO₂. We substitute bacterial BNR with algae-based BNR, which dramatically reduces the size of bacterial aerobic bioreactor and produces algal sludge with much higher carbon content. To function, the algae require CO₂ in excess of what is produced by aerobic bacteria, and hence, the process consumes additional CO₂ generated from offsite industrial combustion processes. Ultimately, this enables three fundamentally transformative outcomes: (1) the excess CO₂ required by the algae makes the process net carbon-negative, (2) the use of algal-BNR versus bacterial-BNR eliminates nitrous oxide emissions, and (3) the higher carbon content algal biomass produces sufficient biogas that the overall process is energy-positive. In addition, the unique process configuration produces pipeline grade biogas (a.k.a., renewable natural gas) along with liquid and solid fertilizer products and Title 22 quality recycled water.

Innovation:

Researchers from UCLA’s Department of Civil and Environmental Engineering have developed a net-energy positive and carbon-negative water recycling and resource recovery process. The approach overcomes the limitation of bacteria-based BNR, while sequestering more CO₂ than it produces while producing high-quality, high-energy biogas. Ultimately, this approach can produce more energy than it consumes (energy-positive) and sequesters CO₂ (carbon-negative), indicating it as a potential next-generation model for state-of-the-art water recycling and resource recovery.

Potential Applications: