Enzyme-Identified Phosphorus Limitation Linked to More Rapid Headloss Accumulation in Drinking Water Biofilters

Comprehensive characterization of aerobic groundwater biotreatment media

Aerobic biotreatment systems can treat multiple reduced inorganic contaminants in groundwater, including ammonia (NH₃), arsenic (As), iron (Fe), and manganese (Mn). While individual systems treating multiple contaminants simultaneously have been characterized and several systems treating one contaminant have been compared, a comparison of systems treating co-occurring contaminants is lacking. This study assessed the treatment performance and microbial communities within 7 pilot- and full-scale groundwater biotreatment systems in the United States that treated waters with pH 5.6-7.8, 0.1-2.0 mg/L dissolved oxygen, 75-376 mg CaCO₃/L alkalinity, < 0.03-3.79 mg NH₃-N/L, < 4-31 µg As/L, < 0.01-9.37 mg Fe/L, 2-1220 µg Mn/L, and 0.1-5.6 mg/L total organic carbon (TOC). Different reactor configurations and media types were represented, allowing for a broad assessment of linkages between water quality and microbial communities via microscopy, biofilm quantification, and molecular methods. Influent NH₃, TOC, and pH contributed to differences in the microbial communities. Mn oxidase gene copy numbers were slightly negatively correlated with the influent Mn concentration, but no significant relationships between gene copy number and influent concentration were observed for the other contaminants. Extracellular enzyme activities, community composition, and carbon transformation pathways suggested heterotrophic bacteria may be important in nitrifying biofilters. Aerobic groundwater biofilters are complex, and improved understanding could lead to engineering enhancements.

Can we shape microbial communities to enhance biological activated carbon filter performance?

A new focus on biofiltration has emerged that aims to shape microbial communities to improve treatment efficacy. It is therefore necessary to understand the linkages between microbial community structure and biofilter function. However, the assembly and interaction of microbial communities in biological activated carbon (BAC) filters are unknown. In this study, we selected one coal-based granular activated carbon (GAC), GAC-13, with simultaneously developed micropore and micro-level macropore volume used for a bench-scale BAC column experiment, and compared it with other coal-based GACs and wood-based GAC in terms of the dissolved organic carbon (DOC) removal and microbial community characteristics. The results showed that there was no difference between the DOC removal efficiency of BAC-13 and the other two coal-based BAC filters with high iodine value in the period dominated by adsorption, while the DOC removal efficiency of BAC-13 (64.7±0.6%) was significantly higher than that of other BAC filters (36.3±0.8-54.1±0.4%) with a difference of 0.3-0.7 mg/L in DOC during the steady state. The bacterial communities were strongly assembled by deterministic rather than stochastic factors, where the surface polarity of GAC had a greater effect on the microbial communities than its physical properties. The corresponding co-occurrence network revealed that microbes in the BAC filter may be more cooperative than competitive. The keystone bacterium Hyphomicrobium, which had a relatively low abundance, contributed 0.3-1% more to the most abundant functions and produced 5-21 proteins/(g·GAC) more than the dominant bacterium Sphingobium. The metaproteomic-based approach could provide more accurate information regarding the contributions of different species to metabolic functions. The pore size distribution of GAC was found to be an important factor in determining BAC filter performance; the most important pore sizes were micropores and micro-level macropores (0.2-10 μm and >100 μm in diameter), and the latter impacted the abundance of keystone species. Overall, our findings provide new insights into shaping microbial communities by optimizing pore size structure to improve BAC performance, especially the abundance of keystone species.

Evaluation of enzyme activity for monitoring biofiltration performance in drinking water treatment

Many water providers monitor adenosine triphosphate (ATP) as an indicator of biological acclimation of their biofilters; however, strong correlations between ATP concentration and filter performance (e.g., organic matter or disinfection by-product precursor removal) are not typically observed. As an alternative, this study evaluated the use of enzyme activity for monitoring biological processes within filters. Recent studies have proposed that enzyme activity may be used as an indicator of biofilter function as it provides a means to quantify biodegradation which may allow for a more accurate measure of degradation potential and to gain a better understanding of biofilter performance. Sampling was completed from full- and pilot-scale biofilters to assess impacts associated with pre-treatments, varying sources waters, as well as pre-treatment and operating conditions. Enzyme activity (carboxylic esterase, phosphatase, ß-glucosidase, α-glucosidase, ß-xylosidase, chitinase, and cellulase) and ATP were measured from the top 5 cm of biofilter media representative of typical full-scale sampling; water quality parameters included dissolved organic carbon (DOC) and disinfection by-products (DBPs): trihalomethane (THM) formation potential (FP), and haloacetic acid FP (HAA FP). Results confirmed that ATP was not a reliable monitoring tool for DOC and DBP FP reduction in biofilters. A strong relationship was observed between esterase activity and DOC reduction; chitinase activity significantly correlated to THM FP reduction for filters treating three different source waters and HAA FP reduction achieved by filters treating the same source water with a range of pre-treatment and backwash conditions. This study showed that enzyme activity may be appropriate for monitoring biological processes within drinking water filters and may act as a surrogate for the removal of organic compounds.

Effective enzyme activity: A proposed monitoring methodology for biofiltration systems with or without ozone

"Effective Enzyme Activity", or simply "Effective Activity", is proposed as a biofiltration monitoring tool which combines enzyme activity with empty bed contact time (EBCT) to quantify biodegradation potential. The primary objective of this study was to evaluate the applicability of the Effective Activity concept for predicting water quality in biofiltration systems. This pilot-scale study evaluated eight different biofilter configurations in order to quantify impacts associated with filter media (anthracite/sand or granular activated carbon), pre-treatment (settled water with or without ozonation) and operating conditions (15- and 30-min EBCT, and backwash with or without chlorine). Microbial characterization included biomass concentration, as measured by adenosine triphosphate (ATP), in addition to esterase and phosphatase activity. Water quality parameters included dissolved organic carbon (DOC), trihalomethane (THM) formation potential (FP), haloacetic acid (HAA) FP, haloacetonitrile (HAN) FP, iodinated DBP FP (THMs and HAAs) and inorganic nutrients (phosphorus and nitrogen). Results confirmed the benefits to treated water quality associated with the application of an ozone residual of 0.5 mg/L, utilization of GAC filter media, eliminating chlorinated backwash, and extending EBCT. This study demonstrated a good relationship between effective esterase activity and reductions in DOC and THM FP, including those systems which incorporate pre-ozonation. As such, this study showed that Effective Activity may be appropriate for relating biomass characterization to treated water quality and highlights the importance of quantifying biomass activity in addition to quantity.

Effects of phosphate and hydrogen peroxide on the performance of a biological activated carbon filter for enhanced biofiltration

Biofilm formation on biofilters can influence their hydraulic performance, thereby leading to head loss and an increase in energy use and costs for water utilities. The effects of a range of factors, including hydrogen peroxide and phosphate, on the performance of biological activated carbon (BAC) and biofilm formation were investigated using laboratory-scale columns. Head loss, total carbohydrates, and proteins were reduced in the nutrient-enhanced, oxidant-enhanced, and nutrient + oxidant-enhanced BAC filters. However, there were no changes in the removal of dissolved organic matter, trihalomethane formation potential, or selected trace organic contaminants. The biofilm formation on polyvinyl chloride and stainless steel coupons using the laboratory biofilm reactor system was lower when the effluent from a nutrient-enhanced column was used, which indicated that there was less biofilm formation in the distribution systems. This may have been because the effluent from the nutrient-enhanced column was more biologically stable. Therefore, enhanced biofiltration could be used not only to reduce head loss in biofilters, but also to delay biofilm formation in distribution systems.