Abstract
Biofilm bioreactors are attracting growing interest in the wastewater industry, as they allow higher cell densities and thus higher reaction rates compared to conventional bioreactors. However, some commonly used nitrifying bacteria, such as Nitrosomonas europaea, are slow-growing and need a prolonged period of time to develop a mature biofilm. Here, a biocoating or "living paint" is introduced, which is a synthetic biofilm made from a colloidal polymer (synthetic latex) binder encapsulating viable nitrifying bacteria at high density. Conventionally, the film formation of biocoatings is achieved by drying a bacteria/latex mixture. However, this fabrication is detrimental to the viability of the encapsulated bacteria because of the osmotic stress induced by desiccation. A nondesiccating film formation process is presented for biocoatings, which exploits two colloid science phenomena: coagulation and wet sintering. Desiccation-sensitive, nitrifying bacteria are employed in the biocoatings to convert NH4+ to NO2- and then NO3-. These biocoatings have a conversion rate (NO2- and NO3- production) of 3 mg N g(-1) d(-1) that is five times higher than in conventionally desiccated biocoatings. The reactivity continues over a period of 1 month. The processing method for these living paints is transformative for wastewater treatment and other applications using delicate, desiccation-sensitive microorganisms.