Biofilter scaling procedures for organics removal: A potential alternative to piloting

Biological Filtration is Resilient to Wildfire Ash-Associated Organic Carbon Threats to Drinking Water Treatment

Elevated/altered levels of dissolved organic matter (DOM) in water can be challenging to treat after wildfire. Biologically mediated treatment removes some DOM; here, its ability to remove elevated/altered postfire dissolved organic carbon (DOC) resulting from wildfire ash was investigated for the first time. Treatment of wildfire ash-amended (low, moderate, high) source waters by bench-scale biofilters was evaluated in duplicate. Turbidity and DOC were typically well-removed (effluent turbidity ≤0.3 NTU; average DOC removal ∼20%) in all biofilters during periods of stable source water quality. Daily DOC removal across all biofilters (ash-amended and controls) was generally consistent, suggesting that (i) the biofilter DOC biodegradation capacity was not deleteriously impacted by the ash and (ii) the biofilters buffered the ash-associated increases in water extractable organic matter. DOM fractionation indicates this was because the biodegradable low molecular weight neutral fractions of DOM, which increased with ash addition, were reduced by biofiltration while humic substances were largely recalcitrant. Thus, biological filtration was resilient to wildfire ash-associated DOM threats to drinking water treatment, but operational resilience may be compromised if the balance between readily removed and recalcitrant fractions of DOM change, as was observed during brief periods herein.

A Critical Remark on the Applications of Gas-Phase Biofilter (Packed-Bed Bioreactor) Models in Aqueous Systems

The principles of gas-phase biofilter systems, modeling, and operations are quite different from liquid-phase biofilter systems. Because of “biofilter” terminology used in both gas and liquid-phase systems, researchers often mistakenly use gas-phase models in liquid-phase applications for the analysis of data and determining kinetic parameters. For example, recent studies show a well-known gas-phase biofilter model, known as Ottengraf–Van Den Oever zero-order diffusion-limited model, is applied for analysis of experimental data from an aqueous biofilter system which is used for the removal of toxic divalent copper [Cu(II)] and chromium (VI). The objective of this research is to present the limitations and principles of gas-phase biofilter models and to highlight the incorrect use of gas-phase biofilter models in liquid-phase systems that can lead to erroneous results. The outcome of this work will facilitate scientists and engineers in distinguishing two different systems and selecting a more suitable biofilter model for the analysis of experimental data in determining kinetic parameters.

Comparison of carrier particles in the gas-liquid-solid inverse fluidised bed bioreactor

The performance and energy consumption of a gas-liquid-solid inverse fluidised bed bioreactor (GLS-IFBBR) using polyethylene (PE) particles with different surface coatings (zeolite, lava rock, activated carbon and multi-plastic) as media for synthetic wastewater treatment were investigated at loading rates of 1.64-3.38 kg COD/(m³·d) and 0.17-0.34 kg N/(m³·d) to determine the optimum carrier media. The results showed that PE coated with other inorganic materials could increase the nutrient removal efficiency at the same influent conditions. Compared with other media, PE coated with zeolite (PEZ) was the optimal carrier particles in this study as reflected by the highest COD and nitrogen removal, stable effluent, low biomass yield at different hydraulic retention times (HRT). In addition, the energy consumption of lavarock-coated PE (PEL) with a highest density was the lowest.

Removal of effluent organic matter with biofiltration for potable reuse: A review and meta-analysis

Biofiltration, historically used for biodegradable organic matter (BOM) removal in drinking water treatment, is being increasingly applied for potable reuse which requires unique characterization. This review and meta-analysis evaluates BOM occurrence as part of bulk wastewater effluent organic matter (EfOM), quantifies the roles of operational parameters to achieve EfOM removal in biofilters, and identifies research gaps which may be fruitful for understanding reuse biofilter performance. Literature data (n = 76) indicates EfOM has a high biodegradable fraction (median 26%), which after typical ozone doses is higher (57%). A biofiltration performance dataset (n = 160 across 42 WWTP effluents) shows that EfOM removal of 35-40% can be expected when design parameters are optimized. Specifically, higher EfOM removal is achieved by adding pre-ozonation and use of biological activated carbon (BAC) media, with comparatively smaller impacts of increasing ozone dose or increasing empty bed contact time under typical scenarios. Combined, these factors strongly correlate with observed EfOM removal (r² = 0.64) after accounting for confounding by adsorptive removal in BAC media with fewer than 20,000 bed volumes treated. Future research that quantifies the occurrence of BOM, biomass activity on filter media, steady-state removal by BAC, and impacts of longer empty bed contact times in potable reuse scenarios could impact optimization strategies to meet or exceed biofilter performance observed to date.

Impact of backwash on biofiltration-related nitrogenous disinfection by-product formation

Previous studies have reported that biofilm extracted from full-scale biofilters can serve as nitrogenous disinfection by-product (N-DBP) precursors. Detached biofilm materials could escape during filter ripening and form N-DBP upon chloramination. This study examined the potential breakthrough of biofilm and N-DBP precursors during filter ripening at two water treatment plants (WTPs). The presence of biofilm material in aqueous samples was estimated by total adenosine triphosphate (tATP) levels; N-DBP formation potential (FP) tests were conducted under uniform formation conditions to quantify N-nitrosodimethylamine (NDMA) and haloacetonitrile (HAN₄) precursors. While tATP peaks in filter effluent were observed post backwash at both WTPs, temporary increases of effluent NDMA FP were only observed during filter ripening where particle-associated NDMA precursors served as the dominant contributor. Overall, biofilters examined in this study demonstrated a consistent removal of NDMA FP regardless of the filter ripening process.

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

Drinking water biofilters can improve water quality by transforming contaminants or their precursors, but they also can develop headloss more rapidly than do abiotic filters. Phosphorus supplementation has been proposed as one strategy to lengthen biofilter run times, but the impact of this strategy in field tests has been mixed. The current bench-scale study found that severe phosphorus limitation, as indicated by a high phosphatase to total glycosidase activity ratio (PHO:GLY), led to 230% higher headloss accumulation rate when particles were loaded onto the biofilters as compared to the same experiment performed under a mild phosphorus limitation. Phosphorus limitation was associated with higher concentrations of extracellular polymeric substances, lower biomass concentrations, a more filamentous biofilm morphology, and increased relative abundance of Hyphomicrobiaceae (a family of stalked bacteria) on the biofilter media. These differences in the biofilm likely contributed to higher headloss. This work suggests that phosphorus supplementation could improve biofilter hydraulics in the field if the biofilter is severely phosphorus limited, which was indicated by a PHO:GLY greater than 154 under the conditions tested in this study.