quantifying-elastic-properties-environmental-biofilms-using-optical

Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography

Biofilms are complex biomaterials comprising a well-organized network of microbial cells encased in self-produced extracellular polymeric substances ...

Black & Veatch

Implementing an aerobic digestion step after anaerobic digestion, referred to as "post aerobic digestion" (PAD), can remove ammonia without the need for an external carbon source and destroy volatile solids. While this process has been documented at the lab-scale and full-scale, the mechanism for N removal and the corresponding microbial community that carries out this process have not been established. This research gap is important to fill because the nitrogen removal pathway has implications on aeration requirements and carbon demand, that is, short-cut N-removal requires less oxygen and carbon than simultaneous nitrification-denitrification. The aims of this research were to (i) determine if nitrite (NO  ) or nitrate (NO  ) dominates following ammonia removal and (ii) characterize the microbial community from PAD reactors. Here, lab-scale PAD reactors were seeded with biomass from two different full-scale PAD reactors. The lab-scale reactors were fed with biomass from full-scale reactors and operated in batch mode to quantify nitrogen species concentrations (ammonia, NH  , NO  , and NO  ) over time. Experimental results revealed that NO  production rates were several orders of magnitude greater than NO  production rates. Indeed, nitrite accumulation rate (NAR) was greater than 90% at most temperatures, confirming that shortcut nitrogen removal was the dominant NH  removal mechanism in PAD. Microbial community analysis via 16S rRNA sequencing indicated that ammonia oxidizing bacteria (AOB) were much more abundant than nitrite oxidizing bacteria (NOB). Overall, this study suggests that aeration requirements for post-aerobic digestion should be based on NO  shunt and not complete simultaneous nitrification denitrification. PRACTITIONER POINTS: AOB are a key feature of PAD microbial communities NOB are present, but in much lower abundance than AOB High nitrite accumulation ratio suggests shortcut nitrite as the main mechanism for nitrogen removal Nitritation in PAD reactors is sustained at temperatures as high as 40°C No ammonia oxidation occurred at 50°C implying different mechanisms of nitrogen removal including ammonia stripping.

Lab-scale data and microbial community structure suggest shortcut nitrogen removal as the predominant nitrogen removal mechanism in post-aerobic digestion (PAD).

Simultaneous nitrification-denitrification (SND) is an advantageous bioprocess that allows the complete removal of ammonia nitrogen through sequential redox reactions leading to nitrogen gas production. SND can govern nitrogen removal in single-stage biofilm systems, such as the moving bed biofilm reactor and aerobic granular sludge system, as oxygen gradients allow the development of multilayered biofilms including nitrifying and denitrifying bacteria. Environmental and operational conditions can strongly influence SND performance, biofilm development and biochemical pathways. Recent advances have outlined the possibility to reduce the carbon and energy consumption of the process via the "shortcut pathway", and simultaneously remove both N and phosphorus under specific operational conditions, opening new possibilities for wastewater treatment. This work critically reviews the factors influencing SND and its application in biofilm systems from laboratory to full scale. Operational strategies to enhance SND efficiency and hints to reduce nitrous oxide emission and operational costs are provided.

Simultaneous nitrification-denitrification in biofilm systems for wastewater treatment: Key factors, potential routes, and engineered applications.

Water resource recovery facilities are faced with stringent effluent phosphorus limits to reduce nutrient pollution. Enhanced biological phosphorus removal (EBPR) is the most common biological route to remove phosphorus; however, many facilities struggle to achieve consistent performance due to limited carbon availability in the influent wastewater. A promising process to improve carbon availability is through return activated sludge (RAS) fermentation via sidestream EBPR (S2EBPR). In this study, a full-scale S2EBPR pilot was operated with a sidestream plus carbon configuration (SSRC) at a carbon-limited facility. A model based on the pilot test was developed and calibrated in the SUMO platform and used to explore routes for improving orthophosphate (OP) effluent compliance. Modeling results showed that RAS diversion by itself was not sufficient to drive OP removal to permit limits of 1 mg L, therefore, other strategies were evaluated. Supplemental carbon addition of MicroC® at 1.90 L min and controlling the phosphorus concentration below 3.5 mgP L in the primary effluent (PE) proved to be valid supplemental strategies to achieve OP removal below 1 mg L most of the time. In particular, the proposed supplemental carbon flow rate would result in an improvement of the rbCOD:P ratio from 17:1 to 26:1. The synergistic approach of RAS diversion and supplemental carbon addition increased the polyphosphate accumulating organisms (PAO) population while minimizing the supplemental carbon needed to achieve consistent phosphorus removal. Overall, this pilot and modeling study shows that joint strategies, including RAS diversion, carbon addition and PE control, can be effective to achieve optimal control of OP effluent.

Impact of operational strategies on a sidestream enhanced biological phosphorus removal (S2EBPR) reactor in a carbon limited wastewater plant.

The Wisconsin Rapids Wastewater Treatment Plant (WRWWTP) is faced with a more stringent effluent phosphorus requirement that will drive capital investment between 2020 and 2025. The facility will need to achieve a monthly average value of 0.36 mg L of total phosphorus (TP). While the facility has sufficient influent carbon to drive a conventional enhanced biological phosphorus removal (EBPR) configuration, the existing infrastructure makes the addition of influent selector zones cost prohibitive. Underutilized aeration basin capacity was repurposed for testing return activated sludge (RAS) fermentation. The WRWWTP began pilot testing of RAS fermentation in April 2021. The facility moved through a series of operational setpoints to optimize phosphorus removal in a sidestream RAS (SSR) configuration, including RAS diversion, decrease of DO in aeration basins and chemical dosing shutoff. One of the key implementations was the addition of cranberry syrup waste to provide additional carbon for RAS fermentation, converting the process to a SSR plus carbon (SSRC) configuration. By the end of the testing period, effluent total phosphorus was averaging less than 0.4 mg L with no chemical addition. A model was developed in the SUMO platform and was used to capture orthophosphate trends during the testing period. The model investigated microbial population dynamics and found that the operational changes including RAS diversion, chemical dosing shutoff and cranberry syrup waste addition impacted the enrichment of phosphorus accumulating organisms (PAO). After performing a sensitivity analysis on hydrolysis parameters, the predicted hydrolysis rate around 1.8-1.9 mg COD g VSS hr was found to match the batch rate testing data. This is the first study where cranberry syrup waste was used to successfully enhance EBPR performance, resulting in 90% TP removal. While further research is needed regarding the composition of the waste matrix and the microbial community composition, this expands the routes for resource recovery in the field of wastewater treatment.

Enhancing resource recovery via cranberry syrup waste at the Wisconsin Rapids WRRF: An experimental and modeling study.

Hydrogel-encapsulated catalysts are an attractive tool for low-cost intensification of (bio)-processes. Polyvinyl alcohol-sodium alginate hydrogels crosslinked with boric acid and post-cured with sulfate (PVA-SA-BS) have been applied in bioproduction and water treatment processes, but the low pH required for crosslinking may negatively affect biocatalyst functionality. Here, we investigate how crosslinking pH (3, 4, and 5) and time (1, 2, and 8 h) affect the physicochemical, elastic, and process properties of PVA-SA-BS beads. Overall, bead properties were most affected by crosslinking pH. Beads produced at pH 3 and 4 were smaller and contained larger internal cavities, while optical coherence tomography suggested polymer cross-linking density was higher. Optical coherence elastography revealed PVA-SA-BS beads produced at pH 3 and 4 were stiffer than pH 5 beads. Dextran Blue release showed that pH 3-produced beads enabled higher diffusion rates and were more porous. Last, over a 28-day incubation, pH 3 and 4 beads lost more microspheres (as cell proxies) than beads produced at pH 5, while the latter released more polymer material. Overall, this study provides a path forward to tailor PVA-SA-BS hydrogel bead properties towards a broad range of applications, such as chemical, enzymatic, and microbially catalyzed (bio)-processes.

Tailoring polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads by controlling crosslinking pH and time.

Anammox-based nitrogen removal and enhanced biological phosphorus removal (EBPR) are increasingly applied for nutrient removal from wastewater, but are typically operated in separate reactors. Here, a novel process for integrated partial nitritation/anammox (PN/A) and EBPR in a single reactor employing integrated fixed film activated sludge was tested. The reactor was fed with mainstream municipal wastewater (5.4 ± 1.3 g COD/g N) at 20 °C for 243 days. Robust ammonium, total inorganic nitrogen, and orthophosphate removal efficiencies of 94 ± 4 %, 87 ± 7 % and 92 ± 7 % were achieved. Nitrite-oxidizing organisms suppression and ammonia-oxidizing organisms retention were achieved via solids retention time control, intermittent aeration, and suspended versus attached biomass population segregation. The contribution of anammox to nitrogen removal increased from 24 % to 74 %. In parallel, a substantial enrichment of Tetrasphaera polyphosphate accumulating organisms was observed. This work demonstrates a novel intensified bioprocess coupling PN/A and EBPR in the same reactor for efficient nutrient removal from wastewater.

Fabrizio Sabba

Black & Veatch

Quantifying Elastic Properties of Environmental Biofilms using Optical Coherence Elastography