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The influence of four main process parameters--solids retention time (SRT), hydraulic retention time (HRT), anoxic-oxic cycling, and carbon-to-nitrogen ratio (C/N ratio)--on poly(hydroxyalkanoate) (PHA) production, while treating brewery wastewater, was studied. Two sets of two-level, three-factor experimental designs were implemented to (1) determine the effects and interactions among process parameters, (2) assess their significance to PHA production, and (3) approximate optimal operational conditions. The HRT and SRT were found to be the crucial operational parameters affecting PHA production. The highest PHA content of 55% (on a cell-weight basis) was produced at a 4-day HRT and 4-day SRT, whereas a maximum PHA concentration of 907 mg/L was obtained at a 2-day HRT and 12-day SRT. The effect of anoxic conditions on PHA production was insignificant. The C/N ratio played a more important role in the PHA concentration in the system than in the PHA content in the biomass.

Polyhydroxyalkanoate (PHA) production was achieved using tomato cannery waste coupled with a mixed microbial culture during wastewater treatment. The two-stage PHA production process comprised a sequencing batch reactor (SBR), operating under a periodic feast-famine regime, to accomplish simultaneously wastewater treatment and selection of PHA-accumulating microbes, followed by a batch reactor for the production of PHA-rich biomass. The SBRs were efficient at removing soluble carbon (84%), ammonia (100%), and phosphorus (76%). Meanwhile, PHA-accumulating microbes were enriched under the SBR operating conditions, and PHA content on a cell-weight basis was within the range 7 to 11% in nonfiltered wastewater and 2 to 8% in filtered wastewater. Subsequently, batch studies were implemented with varying loading rates, ranging from 0.4 to 3.2 food-to-microorganism ratios. A maximum 20% PHA content on a cell-weight basis was obtained. Based on the experimental results, a PHA biosynthesis-degradation kinetic model was developed to (1) aid in the design of a pilot- or full-scale PHA production process coupled with wastewater treatment and (2) determine optimal conditions for harvest of PHA-rich biomass.

Biologically derived polyesters known as polyhydroxyalkanoates (PHAs) represent a potentially "sustainable" replacement to fossil-fuel-based thermoplastics. However, current commercial practices that produce PHA with pure microbial cultures grown on renewable, but refined, feedstocks (i.e., glucose) under sterile conditions do not represent a sustainable commodity. Here, we report on PHA production with a mixed microbial consortium indigenous to an activated sludge process on carbon present in municipal wastewaters. Reactors operated under anaerobic/aerobic and aerobic-only mode and fed primary solids fermenter liquor maintained a mixed microbial consortium capable of synthesizing PHA at 10 to 25% (w/w), while reducing soluble COD by approximately 62 to 71%. More critically, an aerobic batch reactor seeded from the anaerobic/aerobic reactor and fed fermenter liquor achieved approximately 53% PHA (w/w). Results presented suggest that environmentally benign production of biodegradable polymers is feasible. We further used PHA-rich biomass to produce a natural fiber-reinforced thermoplastic composite that can be used to offset advanced wastewater treatment costs.

Occlusion of microorganisms in wastewater particles often governs the overall performance of a disinfection system, and the associated health risks of post-disinfected effluents. Little is currently known on the penetration of chemical oxidants into particles developed in wastewater treatment. In this work, a reactive transport model that incorporates intra- and extra-particle chemical decay, radial intra-particle diffusion, mass transfer resistance at particle surfaces, and non-linear reaction kinetics within a competitive multi-particle size aqueous environment, was used to analyze the penetration of ozone and chlorine into wastewater particles. Individual characteristics from two secondary wastewater treatment facilities were used in model calibration. Simulations revealed that significant ozone transport within particles greater than 6 microm required large initial concentrations to exhaust the preferential reaction with aqueous soluble matter. Chlorinated samples exhibited apparently slower reactions and thus deeper penetration (22-40 microm). Chlorine penetration was less sensitive to variations in the extra-particle reaction and disinfectant concentration than ozone. Model simulations that considered elevated initial concentrations of chemical disinfectants revealed that complete inactivation of all particle size domains was not possible with current disinfection practices (e.g., contact times). Reduction in the health risks associated with wastewater particles requires treatment that efficiently balances particle removal (filtration) and particle inactivation (disinfection).

The fraction of particles with associated coliform bacteria (PAC) in the activated sludge process was evaluated using a 16S rRNA oligonucleotide probe specific to the family Enterobacteriaceae. The PAC was found to decline exponentially with increasing mean cell residence times (MCRTs). The factors influencing the formation of PAC, identified with simplified mass balance relationships. are the concentration of particles, the concentration of dispersed (non-particle associated) coliform bacteria, and the MCRT. The concentration of dispersed coliform bacteria was found to decline with increasing MCRTs. The rate of decline was greater than the typical half-life attributed to endogenous decay, suggesting that other factors (e.g., predation by protozoa) influence the concentration of dispersed coliform bacteria, and subsequently the formation of PAC. Given that the association of targeted organisms with particles adversely impacts the performance of a disinfection system, studies targeted at the fate of organisms other than coliform bacteria in the activated sludge process are of paramount importance in assessing the health risks of post-disinfected effluents.