The overall goal of this study was to develop an appropriate biological process for achieving autotrophic conversion of methane (CH(4)) to methanol (CH3OH). In this study, we employed ammonia-oxidizing bacteria (AOB) to selectively and partially oxidize CH(4) to CH(3)OH. In fed-batch reactors using mixed nitrifying enrichment cultures from a continuous bioreactor, up to 59.89 ± 1.12 mg COD/L of CH(3)OH was produced within an incubation time of 7 h, which is approximately ten times the yield obtained previously using pure cultures of Nitrosomonas europaea. The maximum specific rate of CH(4) to CH(3)OH conversion obtained during this study was 0.82 mg CH(3)OH COD/mg AOB biomass COD-d, which is 1.5 times the highest value reported with pure cultures. Notwithstanding these positive results, CH(4) oxidation to CH(3)OH by AOB was inhibited by NH(3) (the primary substrate for the oxidative enzyme, ammonia monooxygenase, AMO) as well as the product, CH(3)OH, itself. Further, oxidation of CH(4) to CH(3)OH by AOB was also limited by reducing equivalents supply, which could be overcome by externally supplying hydroxylamine (NH(2)OH) as an electron donor. Therefore, a potential optimum design for promoting CH(4) to CH(3)OH oxidation by AOB could involve supplying NH(3) (needed to maintain AMO activity) uncoupled from the supply of NH(2)OH and CH(4). Partial oxidation of CH(4)-containing gases to CH3OH by AOB represents an attractive platform for the conversion of a gaseous mixture to an aqueous compound, which could be used as a commodity chemical. Alternately, the nitrate and CH(3) OH thus produced could be channeled to a downstream anoxic zone in a biological nitrogen removal process to effect nitrate reduction to N(2), using an internally produced organic electron donor.

The reliability and accuracy of in-situ ion selective electrode and ultraviolet (NO) probes have been investigated at four different treatment plants with different operational conditions. This study shows that the mentioned probes tend to compromise their accuracy and trending stability at lower NO of <1.0 mg N/L, which if used as a measuring variable for PI feedback controller for denitrification (biological reduction of nitrate to nitrogen gas), would cause overfeeding the external carbon source. In-situ Clark-type NO sensors, recently introduced for industrial scale use (Unisense Environment) could potentially open a new horizon in the automation of biological processes and particularly denitrification. To demonstrate the applicability of such probes for automation, two in-situ NO probes were used in two treatment plants in parallel with NO-N probes. The effects of operational conditions such as COD/N ratios and the correlation between NO and NO were investigated at those plants. NO production at non-detect dissolved oxygen concentrations and pH of 7-7.2 were found to be a function of influent nitrogen load or the ratio of COD/N. Finally, using an NO probe as a proxy sensor for nitrates is proposed as a measured variable in the PI feedback in the automation of the denitrification process with a NO set point of <1.2 mg N/L).

Soil aquifer treatment (SAT), as a gravity-based wastewater reuse process, is limited by oxygen availability to the microbial community in the soil. Using oxygen from enzymatic degradation of H2O2 to generate hyper-oxygen conditions can exceed solubility limitations associated with aeration, but little is known about the effect of hyper-oxygen conditions on the microbial community and the dominant bio-reactions. This study examined the impact of H2O2 addition on the community structure and process performance, along with SAT depth. Overall, two soil columns were incrementally fed synthetic secondary effluents to simulate infiltration through SAT. The experimental column received 14 mg/L hydrogen peroxide to double the level of natural oxygen available. The microbial kinetics of nitrifiers and heterotrophs were evaluated. We found that all of the H2O2 was degraded within the top 10 cm of the column, accompanied by a higher removal of COD (23 ± 0.25%) and ammonia (31 ± 3%) in comparison to the reference column. Higher nitrogen removal (23 ± 0.04%) was obtained for the whole process using H2O2. Analysis of nitrifiers indicated that ammonia-oxidizing bacteria were most influenced, obtaining higher concentration and abundance when exposed to H2O2. DNA sequencing analysis of samples exposed to H2O2 revealed significant community structure and diversity differences among heterotrophs. This study shows that not only aerobic, but also anoxic, microbial activity and process performance in a SAT system could be accelerated in existing infrastructure with H2O2, which could significantly decrease the associated environmental footprint.

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