| dc.description.abstract | Enhanced biological phosphorus removal (EBPR) has been used for the past 40 years in municipal wastewater treatment to meet declining effluent total phosphorus (TP) limits. While primary fermentation is not new to EBPR, the use of a sidestream fermentation in the Bardenpho configuration of a wastewater treatment plant (WWTP) is a relatively new design that has proven difficult to model (Barnard et al. 2017, Houweling et al. 2010). Sidestream fermentation involves diverting a portion of the return activated sludge (RAS) or anaerobic mixed liquor to a sidestream bioreactor, which allows activated sludge time to settle and collect, allowing volatile fatty acids (VFA) production to take place (Houweling et al. 2010). This configuration is favored over primary fermentation because it helps overcome shortcomings of primary fermentation to allow for consistently high TP removal despite low or fluctuating VFA:TP ratio of the plant's influent (Barnard et al. 2017). Polyphosphate accumulating organisms (PAOs) and denitrifying polyphosphate accumulating organisms (dPAOs) are responsible for the removal of phosphate from wastewater in the EBPR process. The sidestream fermenter with its increased VFA:TP ratio should select for dPAOs, which are preferred over PAOs because of their ability to remove P and nitrogen from wastewater simultaneously. An enriched dPAO population has the potential to reduce operational costs of plants because of the savings on oxygen and carbon sources as compared to EBPR plants with only a PAO community. The objective of this study was the optimization of a full-scale sidestream fermenter EBPR WWTP to select for dPAOs. The WWTP is a 2.5 annual MGD three-stage Bardenpho plant with a mixed liquor suspended solids (MLSS) sidestream fermenter. The WWTP operates without effluent filtration or the addition of carbon or ferric chloride to assist with biological nutrient removal (Kobylinski et al. 2019). Based on preliminary correlations of operating data, it is hypothesized there are four contributing factors to the optimization of an EBPR WWTP with sidestream fermentation: 1) the readily biodegradable chemical oxygen demand (rbCOD):TP ratio, 2) oxidation-reduction potential (ORP), 3) volatile fatty acids (VFA) concentration, and 4) the solids retention time (SRT) of the fermenter. Of these four parameters, only SRT can be easily affected by WWTP operators. Over the 15 weeks of this experiment, the SRT of the WWTP was stepwise increased every three weeks to test SRTs from ~1.1 days to ~2.4 days. The SRT of the fermenter was held at approximately 1.1 days, 1.3 days, 1.5 days, 2.0 days, and 2.4 days for three weeks each to reach stabilization and conduct batch sludge activity tests for specific oxygen uptake rate (SOUR), max nitrification rate, dPAO activity, and sludge volume index (SVI). Operational data was collected for the duration of the experiment from both inline probes and daily and weekly lab tests. Finally, microbial analysis (flourescent in situ hybridization (FISH), qPCR, and Neisser staining) was conducted on grab samples collected throughout the 15-week experiment to investigate community shifts in PAOs and GAOs. All three types of data collected in this experiment showed a positive correlation with increased SRT. The operational data showed a statistically significant correlation between the formation of VFAs and the fermenter SRT between 1.1 and 2.4 days. The activity data was the least correlated with the change in fermenter SRT. The microbial data from fluorescent in situ hybridization (FISH) and quantitative polymerase chain reaction (qPCR) showed very promising results with a strong correlation to the increase in PAOs in the WWTP and the increasing SRT of the fermenter. Based on the results of this study, a sidestream fermenter should be operated around an SRT of 2.0 days to optimize VFA creation to select for PAOs that complete EBPR. These results are at the higher end of previous work by Barnard et al. in 2017, which put the ideal SRT between 1.5 and 2 days (Barnard et al. 2017). This study confirmed that a WWTP with low influent rbCOD:TP ratio could still reach low P effluent levels through EBPR without the added expense of supplemental carbon by adjusting the SRT of the sidestream fermenter to create the VFAs necessary to select for organisms that remove phosphorous from wastewater (WW). | |
