Response of a sludge-minimizing lab-scale BNR reactor when the operation is changed to real primary effluent from synthetic wastewater

Responses of Exogenous Bacteria to Soluble Extracellular Polymeric Substances in Wastewater: A Mechanistic Study and Implications on Bioaugmentation

Compared with the chemically defined synthetic wastewater (SynWW), real wastewater has been reported to exhibit distinct effects on microbial community development. Whether and how soluble microbial products in real wastewater contribute to different effects of synthetic and real wastewater on the fate of exogenous bacteria remains elusive. In this study, using a model wastewater bacterium Comamonas testosteroni, we first examined the influences of microfiltration filter-sterilized real wastewater (MF-WW) and SynWW on the retention of C. testosteroni in established wastewater flocs during bioaugmentation. In bioreactors fed with MF-WW, augmentation of C. testosteroni to wastewater flocs resulted in a substantially higher abundance of the augmented bacterial cells than those fed with SynWW. To identify the soluble microbial products in MF-WW contributing to the observed differences between bioaugmentation reactors fed with MF-WW and SynWW, we examined the effect of MF-WW and SynWW on the growth, floc formation, and biofilm development of C. testosteroni. When C. testosteroni grew in MF-WW, visible flocs formed within 2 h, which is in contrast to cell growth in SynWW where floc formation was not observed. We further demonstrated that the observed differences were mainly attributed to the high molecular weight fraction of the soluble extracellular polymeric substances (EPS) in MF-WW, in particular, proteins and extracellular DNA. The DLVO analysis suggested that, in the presence of soluble EPS, the bacterial cell surface exhibits an increased hydrophobicity and a diminished energy barrier, leading to irreversible attachment of planktonic cells and floc formation. The RNA-seq based transcriptional analysis revealed that, in the presence of soluble EPS, genes involved in nonessential metabolisms were downregulated while genes coding for Cco (cbb3-type) and Cox (aa3-type) oxidases with different oxygen affinities were upregulated, facilitating bacterial survival in flocs. Taken together, this study reveals the mechanisms underlying the contribution of soluble EPS in real wastewater to the recruitment of exogenous bacteria by microbial aggregates and provides implications to bioaugmentation.

A new sulfidogenic oxic-settling anaerobic (SOSA) process: The effects of sulfur-cycle bioaugmentation on the operational performance, sludge properties and microbial communities

In-situ sludge reduction can be achieved by inserting an anaerobic side-stream reactor in the sludge return line of the conventional activated sludge (CAS) process. This modified oxic-settling-anaerobic (OSA) process can reduce sludge production by 30-50% through feast-fast alternating conditions. This paper proposes a new bioprocess called the sulfidogenic oxic-settling anaerobic (SOSA) process with OSA configuration and the addition of sulfate in side-stream reactor. The new bioprocess augments the conventional anaerobic/anoxic/aerobic feast-fast bioconversions with sulfur biochemical transformations (i.e. sulfate reduction and sulfur-oxidizing autotrophic denitrification). A lab-scale SOSA process was operated for 260 days in parallel with the anoxic/oxic (AO) CAS process and the conventional OSA process as control systems. Based on the experimental results, the feasibility of the new SOSA process was evaluated, and the effects of sulfur bioaugmentation on the effluent quality, sludge reduction, sludge physico-chemical properties and microbial communities were examined. The SOSA process i) removed 98% of the organics (chemical oxygen demand, COD) and 99% of the ammonia present with a lower observed sludge yield (0.204 g TSS/g COD_removed) than those of the OSA and AO processes (0.292 and 0.473 g TSS/g COD_removed respectively), ii) denitrified 18% and 6% more nitrogen to dinitrogen gas than did the CAS and OSA processes respectively, iii) produced sludge with improved settleability and dewaterability, iv) encouraged sludge decomposition with greater destruction of extracellular polymeric substances and v) enriched sulfur-cycle related and hydrolytic/fermentative bacteria. The possible mechanisms of sulfur augmentation and limitations of the present study are also discussed.

Strength and Water Purification Properties of Environment-Friendly Construction Material Produced with the (D)PAOs and Zeolite

The goal of this study was to improve the water purification performance of secondary concrete products that can be used in rivers and streams. To this end, mortar and porous concrete were produced by adding both de-nitrifying phosphate accumulating organisms ((D)PAOs) and zeolite, and their mechanical properties and water purification performance were analyzed. The compression strength test results showed that the strength was the highest when the mixing ratios of (D)PAOs and zeolite were set to 10% and 5%, respectively. For better contaminant adsorption, however, the optimal mixing ratio of zeolite was determined to be 10%. When the mixing ratio of (D)PAOs was set to 10%, the concentrations of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) decreased by 57.9% and 89.9%, respectively, after seven days of immersion when compared to the initial concentrations. When compared to plain porous concrete, the total nitrogen (T-N) and total phosphorus (T-P) removal ratios of the develop concrete were 11.0% and 17.8% higher, respectively. When the mixing ratios of (D)PAOs and zeolite were set to 10% for both, the T-N and T-P removal ratios were determined to be 86.3% and 88.1%, respectively, while the BOD and COD concentrations were 2.668 mg/L and 16.915 mg/L, respectively. In simpler terms, the water purification performance was up to 17% higher in the concrete mixed with both 10% (D)PAOs and 10% zeolite than in the concrete mixed with 10% (D)PAOs only. Overall, the optimal mixing ratios of (D)PAOs and zeolite to maximize the water purification effect of secondary concrete products while maintaining their strengths equivalent to or higher than those of their corresponding plain concrete products are considered to be 10% for both.

Excess sludge disruption and pollutant removal from tannery effluent by upgraded activated sludge system

This study proposed a maintenance metabolism based upgraded activated sludge as MANODOX system that restricts excess biosludge generation from high strength real tannery effluent. The MANODOX experimental demonstration has been done using a sequenced operational arrangement of a MBBR, anaerobic digester, and oxidation ditch connected to CAS reactor, discussed in detail manner. Experimental trends revealed a prominently lower sludge yield upto 0.271 gVSS/gCOD (72% overall sludge reduction) that corresponds to parallel run CAS (0.92 gVSS/gCOD). MANODOX implementation confirmed high quality treated effluent with prominent COD and suspended solids reduction upto 97.1% and 96% respectively. The biodegradability observation was further supported by anaerobic and aerobic batch digestion analysis. The variation of soluble component turbidity analysis reflects the enriched non-flocculating predatory microbial population appears to may have been responsible for sludge reduction. MANODOX system provided a sustainable practical alternative for under capacity activated sludge based treatment facilities for a variety of wastewater types.

Overall effect of carbon production and nutrient release in sludge holding tank on mainstream biological nutrient removal efficiency

The potential of hydrolysis/fermentation of activated sludge in sludge holding tank (SHT) to produce additional carbon for the biological nutrient removal (BNR) process was investigated. The study was conducted in anaerobic batch tests using the BNR sludge (from a full-scale Westside process) and the mixture of BNR sludge with conventional non-BNR activated sludge (to have higher biodegradable particulate chemical oxygen demand (bpCOD) in sludge). The BioWin 4.1 was used to simulate the anaerobic batch test of the BNR sludge. Also, the overall effect of FCOD production and nutrient release on BNR efficiency of the Westside process was estimated. The experimental results showed that the phosphorous uptake of sludge increased during hydrolysis/ fermentation condition up to the point when poly-P was completely utilized; afterwards, it decreased significantly. The BioWin simulation could not predict the loss of aerobic phosphorous uptake after poly-P was depleted. The results showed that in the case of activated sludge with relatively higher bpCOD (originating from plants with short sludge retention time or without primary sedimentation), beneficial effect of SHT on BNR performance is feasible. In order to increase the potential of SHT to enhance BNR efficiency, a relatively low retention time and high sludge load is recommended.

New insights into comparison between synthetic and practical municipal wastewater in cake layer characteristic analysis of membrane bioreactor

In previous studies, cake layer analysis in membrane bioreactor (MBR) was both carried out with synthetic and practical municipal wastewater (SMW and PMW), leading to different results. This study aimed to identify the comparison between SMW and PMW in cake layer characteristic analysis of MBR. Two laboratory-scale anoxic/oxic MBRs were operated for over 90days with SMW and PMW, respectively. Results showed that PMW led to rough cake layer surface with particles, and the aggravation of cake layer formation with thinner and denser cake layer. Additionally, inorganic components, especially Si and Al, in PMW accumulated into cake layer and strengthened the cake layer structure, inducing severer biofouling. However, SMW promoted bacterial metabolism during cake layer formation, thus aggravated the accumulation of organic components into cake layer. Therefore, SMW highlighted the organic components in cake layer, but weakened the inorganic functions in practical MBR operation.

Activated sludge mass reduction and biodegradability of the endogenous residues by digestion under different aerobic to anaerobic conditions: Comparison and modeling

This study was performed to identify suitable conditions for the in-situ reduction of excess sludge production by intercalated digesters in recycle-activated sludge (RAS) flow. The objective was to compare and model biological sludge mass reduction and the biodegradation of endogenous residues (XP) by digestion under hypoxic, aerobic, anaerobic, and five intermittent-aeration conditions. A mathematical model based on the heterotrophic endogenous decay constant (bH) and including the biodegradation of XP was used to fit the long-term data from the digesters to identify and estimate the parameters. Both the bH constant (0.02-0.05 d(-1)) and the endogenous residue biodegradation constant (bP, 0.001-0.004 d(-1)) were determined across the different mediums. The digesters with intermittent aeration cycles of 12 h-12 h and 5 min-3 h (ON/OFF) were the fastest, compared to the aerobic reactor. The study provides a basis for rating RAS-digester volumes to avoid the accumulation of XP in aeration tanks.