Engineered Anammox Biofilms for Low-Energy Wastewater Remediation and Environmental Protection

According to the UK Environment Agency, there are continuing problems with the discharge of NH4+ and NO3- from wastewater to the environment, causing harm to aquatic ecology, drinking water resources, and human health. In municipal wastewater treatment, combinations of nitrifying and denitrifying bacteria are commonly used to convert NH4+ to NO3- and then to N2 gas. But the aerobic NH4+ oxidation processes consume huge amounts of energy (for aeration) and are costly. An attractive alternative is to use anaerobic ammonia oxidation (annamox) bacteria, which provide a "shortcut" by converting NH4+ and NO2- directly to N2. A key benefit is that anammox processes are anaerobic, meaning no energy-consuming aeration is needed. A partial nitrification/anammox process is estimated to require 0.3 g-O2/g-N - much less than the 4.57 g-O2/g-N used in conventional nitrification/nitrification. Moreover, annamox uses no external organic carbon, thus reducing the energy consumption by 60% plus saving cost on external chemicals.

Although anammox is a promising alternative to tackle an acute environmental problem, its application is currently limited to high NH4+ concentration wastewater (side-stream from sludge digestate). Applications to mainstream sewage treatment and nature-based solutions (e.g., constructed wetland) poses several challenges, especially how to immobilize the anammox bacteria and maintain their activity. Naturally-occurring biofilms are the most suitable "habitat" for anammox growth, due to long retention times, protective matrix, and intra-/inter-species interactions. Unfortunately, natural anammox biofilm growth is slow. Mature anammox biofilms easily disintegrate and lose their activity, especially in the UK's low temperature wastewater.

Our breakthrough idea is to develop a type of "synthetic biofilm" by encapsulating anammox bacteria in a water-based polymer to make an engineered "biocoating." We hypothesise that our biocoatings will protect the bacteria mechanically, will increase their adhesion to carriers inside of bioreactors, and will seed natural biofilm growth on their surfaces. We will add electrically-conducting nanoparticles (ECNP), e.g. nanowires and C nanotubes, to provide bridges to stimulate extra-cellular electron transfer (EET) to accelerate the NH4+ oxidation rates in the anammox process. We speculate the ECNP will provide conducting pathways to external electron acceptors (other than NO2-), thereby halting the production of the harmful greenhouse gas, N2O.

There are no prior reports of anammox biocoatings, which confirms the research novelty. We have recent experience with other bacterial species in biocoatings.