The effect of anaerobic-aerobic and feast-famine cultivation pattern on bacterial diversity during poly-β-hydroxybutyrate production from domestic sewage sludge

Combined high-rate contact stabilization and chemically enhanced primary treatment for enhanced recovery of organic matter and biogas from sewage

This study examined integrating high-rate contact stabilization (HRCS) and chemically enhanced primary treatment (CEPT) for wastewater to improve the carbon recovery rate (CRR). Enhancing chemical oxygen demand (COD) removal efficiency was hypothesized to improve the CRR. The evaluation covered serial HRCS-CEPT, serial CEPT-HRCS, and single-stage carbon recovery (Single-CR). The COD removal efficiencies for individual HRCS and CEPT were 50.3 % and 56.2 %, respectively. The serial CEPT-HRCS system failed in the HRCS process due to poor settling, resulting in microbial washout. However, the serial HRCS-CEPT system achieved the highest COD removal efficiency (84.5 %). The Single-CR system exhibited the highest CRR of 0.780 ± 0.083 g-CODCH4/g-CODinf, identifying it as the most promising process for energy-positive wastewater treatment. The selective pressure in the high-rate system resulted in a simplified and specialized bacterial community, mainly comprising microorganisms with high polyhydroxyalkanoate storage capacity, such as Lactococcus sp., Enterobacter sp., and Acinetobacter sp.

Enhancing the efficacy of synthesising PHA from nitrogen-limited activated sludge using magnetic field

Polyhydroxyalkanes (PHA) is a biodegradable biopolyester. In this study, we introduced the biological effects of magnetic field into a sequencing batch reactor (SBR) for PHA production to evaluate the effect of different strength of magnetic field on the efficacy of PHA synthesis by activated sludge and used the magnetic field to enhance the PHA synthesis capacity of nitrogen-limited activated sludge and to optimise the percentage of the content of the two monomers in PHA. The results showed that the magnetic field of appropriate strength was favourable to increase the production of PHA and to increase the percentage of PHV. In addition, microbial community analysis showed that there was an obvious succession of key functional bacteria under different strength of magnetic field. The highest PHA accumulation was achieved after the magnetic field of 16 mT, which reached 57.65% of the dry weight of sludge. In addition, the PHV monomers were more sensitive to the response of the magnetic field, and the magnetic field of 8mT and 16mT positively promoted the synthesis of PHV. It is worth noting that too high a magnetic field would have an inhibitory effect on the synthesis of PHA.

Aerobic digestibility of waste aerobic granular sludge (AGS) assessed by respirometry, physical-chemical analyses, modeling and 16S rRNA gene sequencing

Research has evolved on aerobic granular sludge (AGS) process, but still there are very few studies on the treatment of excess AGS sludge, with almost none considering its aerobic digestion. Here therefore, the aerobic digestibility of typical AGS sludge was assessed. Granules were produced from acetate-based synthetic wastewater (WW) and were subjected to aerobic digestion for 64 d. The stabilization process was monitored over time through physical-chemical parameters, oxygen uptake rates (OUR) and 16S rRNA gene sequencing. The microbial analyses revealed that the cultivated granules were dominated by slow-growing bacteria, mainly ordinary heterotrophic organisms with potential for polyhydroxyalkanoates (PHA) aerobic storage (PHA-OHOs), polyphosphate and glycogen accumulating organisms (PAOs and GAOs), fermentative anaerobes and nitrifiers (AOB and NOB). Differential abundance analysis of the bacterial data (before versus after digestion) discriminated between the most vulnerable microbiome genera and those most resistant to aerobic digestion. Furthermore, modeling of the stabilization process determined that the endogenous decay rate constant (bH) for the heterotrophs present in the granules was notably low; bH = 0.05 d-1 (average), four times less than for common activated sludge (AS), which is rated at 0.2 d-1. For first time, the research reveals another important feature of AGS sludge, i.e. the slow-decaying character of its bacteria (along with their known slow-growing character). This results in slower stabilization, need of bigger digesters and reconsideration of the specific OUR limits in biosolids regulations (SOUR limit of 1.5 mg/gTSS.h), for waste AGS compared to conventional waste AS. The study suggests that aerobic digestion of waste AGS (fully-granulated) could differ from that of conventional AS. Future work is needed on aerobic digestibility of real AGS sludges from municipal and industrial WWs, compared to synthetic WWs.

Effect of enrichment conditions of secondary feeding on the synthesis of polyhydroxyalkanoates (PHAs) by activated sludge

Polyhydroxyalkanoates (PHAs) are biodegradable plastics with great performance and development prospects. However, their traditional anaerobic/aerobic enrichment process requires a high concentration of dissolved oxygen (DO), resulting in high energy consumption. In this study, an anaerobic/oxygen-limited with secondary feeding enrichment mode was used to enhance the synthesis of PHAs while reducing energy consumption. The enrichment process of PHAs-synthesizing bacteria lasted up to 100 days, and the experiment was conducted to investigate the change of the PHAs synthesizing ability of the system in this mode by detecting the PHAs content and community distribution of the activated sludge under different stages. Under these conditions, the system enriched two major genera of PHAs-synthesizing bacteria, Thauera (30.21%) and Thiothrix (21.30%). The content of PHAs in the sludge increased from 4.51% to 30.87% and was able to achieve a concomitant increase in poly(3-hydroxyvalerate) (PHV) monomer content. After nitrogen limitation (C/N = 150) treatment, the content of PHAs reached 63.05%. The results showed that the enrichment mode of anaerobic/oxygen-limited with secondary feeding could enrich more PHAs-synthesizing bacteria and significantly increase the synthesis amount of PHAs, which revealed the great potential of this mode in solid waste value-added and reduce the production cost of PHAs and could provide a theoretical basis for the production of PHAs from activated sludge.

Mechanisms of persistence and impact of ordinary heterotrophic organisms in aerobic granular sludge

The stability of granules, contaminant removal and microbial structure of an aerobic granular sludge (AGS) process were investigated with a focus on ordinary heterotrophic organisms (OHOs). Long-term stable granules and high removals of COD (97 %), NH₄⁺ (98 %), P (85 %) and total N (77 %) were achieved. Sequencing analyses identified 6.6 % of phosphorus-accumulating organisms in the sludge, concordant with the observed bio-P removal capacity. However, OHOs were the most abundant bacteria in the sludge (70-93 %) without resulting in unstable aggregates. Under current dogmas of microbial competition in activated sludge, it seemed contradictory that OHOs could persist in the long term in the AGS where COD was depleted beginning in the anaerobic phase. Microbial analyses showed that OHOs could survive in granules by micropredation, proteolysis, fermentation and EPS consumption. Heterotrophic-nitrification/ aerobic-denitrification was an active pathway in the AGS. These findings contribute to a better understanding of microbial competition in AGS and its stability.

Consistency between the metabolic performance of two aerobic granular sludge systems and the functional groups of bacteria detected by amplicon sequencing

Two sequential batch reactors (R1 and R2) of aerobic granular sludge (AGS) were inoculated with activated sludge of different origins. The objective was to investigate the granulation and the consistency between the structure of the microbial communities (16S rRNA amplicon sequencing) in each reactor and their metabolic performance (removal of C, N, and P). Both reactors were fed with acetate-based synthetic wastewater, targeting an anaerobic-aerobic cycle reputed to favor the phosphorus- and glycogen-accumulating organisms (PAO and GAO). Stable granulation was achieved in both reactors, where, instead of PAO, the dominant genera were ordinary heterotrophic organisms (OHO) such as Thauera, Paracoccus, and Flavobacterium known for their high capacity of aerobic storage of polyhydroxyalkanoates (PHA). Generally, there was good consistency between the metabolic behavior of each reactor and the bacterial genera detected. Both reactors showed high removals of C and complete nitrification (Nitrosomonas and Nitrospira detected) but a low level of simultaneous nitrification-denitrification (SND) during the aerated phase. The latter causes that nitrates were recycled to the initial phase, in detriment of PAO selection. Meanwhile, the study showed that selecting slow-growing OHOs (with aerobic storage capacity) favors stable granulation, revealing an alternative AGS technology for C and N removal.

Pilot-scale and mechanistic study of the degradation of typical odors and organic compounds in drinking water by a combined UV/H2O2-BAC process

Odor problems are challenging issues in water treatment. Advanced oxidation has a significant degradation effect on these odors; however, some issues, such as oxidant residues and disinfection byproducts, exist in the use of advanced oxidation in actual water treatment. Because of the above issues, a combined advanced oxidation process has emerged-the UV/H₂O₂ -biological activated carbon (BAC) process can play a strong oxidizing role in advanced oxidation and uses the physical adsorption and biological effects of activated carbon. However, there have been few studies on the odor degradation mechanism and characteristics of activated carbon biofilms in actual water treatment. This paper systematically studied the organic and odor substances removal effects and mechanism of a pilot combined UV/H₂O₂-BAC process. The results showed that UV/H₂O₂-BAC technology had a good removal effect on odor substances under long-term stable operation. The concentrations of geosmin (GSM) and 2-methylisoborneol (2-MIB) after systemic treatment were below 5 ng/L. The removal rates of DOC, UV₂₅₄ and H₂O₂ by the combined process were 53.60%, 73.08% and 60.20%, respectively. The results of full-scan determination of GSM and 2-MIB degradation by gas chromatography-mass spectrometry (GC-MS) were consistent with those of front-track analysis. The diversity, richness and evenness of microorganisms in the lower activated carbon layer were higher than those in the middle and upper activated carbon layers. The greater the difference in the carbon layer height was, the greater the difference in the biological community structure.

Achieving polyhydroxyalkanoate production from rubber wood waste using mixed microbial cultures and anaerobic-aerobic feeding regime

In the past few years, creating value-added products has become the best choice to pretreat biomass waste. For instance, the fermentable sugar obtained after pretreatment bioconversion into valuable bioproducts, biopolymer as a typical representative, has become a potential strategy. In particular, the production of biopolymer polyhydroxyalkanoate (PHA) by mixed microbial cultures in waste activated sludge can be regarded as a promising alternative to traditional petrochemical plastics. In this study, the enzymatic hydrolysate of rubber wood was utilized as substrate to explore the optimal process conditions for the accumulation of PHA under anaerobic-aerobic mode. The results showed that longer operation cycle (24 h), suitable anaerobic duration (3.5 h) and secondary feeding regimen (secondary addition without draining liquid) were more beneficial to PHA production. After accumulation, the highest PHA production, PHA storage yield (Y_PHA/S) and ratio to cell dry weight (CDW) reached 929.8 mg COD·L^-1, 0.24 g COD/g COD and 0.31 g PHA/g CDW, respectively. The Y_PHA/S values were similar to the previous reported 0.22 ∼ 0.24 g COD/g COD. The results demonstrated that the secondary feeding regimen was an effective approach to improve the production of PHA with rubber wood enzymatic hydrolysate as substrate.

Poly(3-hydroxypropionate): Biosynthesis Pathways and Malonyl-CoA Biosensor Material Properties

Many single-use non-degradable plastics are a threat to life today, and several polyhydroxyalkanoates (PHAs) biopolymers have been developed in the bioplastic industry to place petrochemical-based plastics. One of such is the novel biomaterial poly(3-hydroxypropionate) [poly(3HP)] because of its biocompatibility, biodegradability, and high yield synthesis using engineered strains. To date, many bio-polymer-based functional composites have been developed to increase the value of raw microbial-biopolymers obtained from cheap sources. This review article broadly covers poly(3HP), a comprehensive summary of critical biosynthetic production pathways comparing the yields and titers achieved in different Microbial cell Factories. This article also provides extensive knowledge and highlights recent progress on biosensors' use to optimize poly(3HP) production, some bacteria host adopted for production, chemical and physical properties, life cycle assessment for poly(3HP) production using corn oil as carbon source, and some essential medical applications of poly(3HP).

Effects of carbon sources and operation modes on the performances of aerobic denitrification process and its microbial community shifts

Carbon source, operation mode and microbial species have great effects on the synthesis of poly-β-hydroxybutyrate (PHB) which has been identified as the key issue for aerobic denitrification process. In this study, an aerobic denitrification SBR was operated under anoxic/oxic mode and completely oxic mode with the carbon source of CH₃COON_a and CH₃CH₂CH₂COON_a, respectively. Total nitrogen (TN) removal efficiencies, PHB content in activated sludge, production of nitric oxide (NO) and nitrous oxide (N₂O) of the process were investigated in great detail. The main results obtained from the trial were: (1) the average TN removal was in the range of 86.11%-90.05%; (2) the maximum TN removal efficiency and the maximum PHB content of the process being achieved when the carbon source of CH₃CH₂CH₂COON_a was applied under anoxic/oxic mode; (3) in case of CH₃COON_a as the carbon source, the concentrations of NO and N₂O in the bulk liquid were ∼0.4 mg/L and ∼0.02 mg/L, respectively, while in case of CH₃CH₂CH₂COON_a, N₂O of ∼0.2 mg/L and NO of ∼2.5 mg/L were recorded and the latter was decreased to ∼1.0 mg/L at the end of the cycle; (4) no obvious dominant genus in case of using CH₃COON_a, while Plasticicumulans sp. being the major microbial community when using CH₃CH₂CH₂COON_a. Overall, the effect of carbon source on microbial community is obvious. Nevertheless, operation mode affects the PHB synthesis, while PHB plays an important role in aerobic denitrification process for achieving a relatively high TN nitrogen removal efficiency. CH₃COON_a is a better carbon source for aerobic denitrification compared with CH₃CH₂CH₂COON_a.

Sludge reduction and microbial structures of aerobic, micro-aerobic and anaerobic side-stream reactor coupled membrane bioreactors

An anoxic/oxic membrane bioreactor (MBR) and three side-stream reactor (SSR) coupled membrane bioreactors were operated in parallel to investigate effects of dissolved oxygen (DO) level in SSR on sludge reduction and microbial community structure of SSR-MBRs. The four MBRs were equally efficient in COD and ammonium nitrogen removal. The anaerobic and micro-aerobic SSR favored nitrogen removal through denitrification, simultaneous nitrification and denitrification and autochthonous substrate release as carbon source. The micro-aerobic SSR achieved greatly higher sludge reduction efficiency (61.1%) than anaerobic (37.3%) and aerobic SSR (7.9%). Micro-aerobic SSR obtained the highest endogenous decay constant (0.035 d^-1) compared to anaerobic (0.023 d^-1) and aerobic SSR (0.015 d^-1). High-throughput sequencing results revealed that anaerobic SSR enriched hydrolytic and fermentative bacteria, aerobic environment favored the growth of slow-growing bacteria, and micro-aerobic SSR stimulated biological activities of both anaerobic and aerobic bacteria.