Anaerobic digestion, an economic and energy-efficient biological process, is extensively applied in the treatment of a variety of wastewater streams and organic wastes. However, the ineffective ...mineralization of degradation-resistant organic wastes is considered a limiting factor for this promising technology, and has prevented it from being widely adopted for the anaerobic treatment of chemical-industrial organic wastewater. In this work, the advantages and benefits of anaerobic digestion and those conventional physical/chemical/biological methods are compared. This review also suggests the current challenges and barriers to the application of anaerobic digestion to the treatment of chemical-industrial organic wastewater by considering some typical degradation-resistant organic wastes as examples. Design improvements are required to enhance the degradation from refractory organics to fermentable organics. The applications of the up-flow anaerobic sludge blanket, anaerobic membrane bioreactor and their derivatives are highly recommended in the anaerobic treatment of chemical-industrial organic wastewater. While some state-of-the-art physical/chemical technologies have been widely reported and are currently applied in anaerobic treatment of chemical-industrial organic wastewater, high energy consumption and low efficiency of these processes is an obstacle to their smooth operation and presents clear difficulties. Therefore, this work provides some perspectives for future applications and practical advice for improving and enhancing the hydrolysis step of those degradation-resistant organic wastes. Synergistic processes, such as the co-culturing method, co-digestion and nitrate-reducing anaerobic digestion are suggested as a means to achieve the effective anaerobic treatment of chemical-industrial organic wastewater and sustainable regeneration of cleaner production.
Anammox achieves chemoautotrophic nitrogen removal under anaerobic and anoxic conditions and is a low-carbon wastewater biological nitrogen removal process with broad application potential. However, ...the physiological limitations of AnAOB often cause problems in engineering applications, such as a long start-up time, unstable operation, easily inhibited reactions, and difficulty in long-term strain preservation. Exogenous additives have been considered an alternative strategy to address these issues by retaining microbes, shortening the doubling time of AnAOB and improving functional enzyme activity. This paper reviews the role of carriers, biochar, intermediates, metal ions, reaction substrates, redox buffers, cryoprotectants and organics in optimizing anammox. The pathways and mechanisms of exogenous additives, which are explored to solve problems, are systematically summarized and analyzed in this article according to operational performance, functional enzyme activity, and microbial abundance to provide helpful information for the engineering application of anammox.
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•Studies on the effects of exogenous additives on anammox are reviewed.•The promotion mechanisms of anammox exogenous additives are discussed.•Future research prospects for anammox exogenous additives are outlined.
•Chemical crystallization was the main factor in the HAP process.•Biomineralization by EPS played a minor role in Ca and P removal.•Granules promoted Ca and P removal as crystal seeds based on the ...Lamer model.•Anammox-HAP coupled granules exhibited enhanced buffering capacity.•Ion competition, exchange and adsorption were observed in anammox-HAP granules.
The potential of the formation of anammox-hydroxyapatite (HAP) granule composites as a cost-effective approach to removing nitrogen and phosphorus in the treatment of wastewater has been recently reported. Before these annamox granules, which consist of an anammox biofilm layer and an HAP crystallizing layer, can be used in applications, the formation mechanism of hydroxyapatite (HAP) encapsulation in the granules needs to be further studied. In this work, the role of extracellular polymeric substance (EPS) secreted by microorganisms and HAP core in Ca and P removal in anammox-HAP coupled granular sludge was investigated. According to the Lamer model, it is possible that the nucleation time of the granules becomes shorter as the crystal seeds. The enhanced buffering capacity of the granules was 0.08 mmol-H+ SS-g−1 with the pH kept above 6.5 for a comfortable environment for anammox. The results of this study show that ion competition and exchange, mainly between cations of Ca2+ and Mg2+ and between anions of PO43− and CO32−, affects the precipitation process. The results of this study indicate that the addition of granule crystal seeds can be used as a strategy to hasten the anammox process, and therefore accelerate the overall process.
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•The N and P removal were achieved in P concentration high than 11.4 mg L−1.•The sludge bulking was an omen for floatation.•Increased EPS resulted in the deterioration of granules.•The main reason of ...floatation was unreleasable gas bubbles attached granules.•A sufficient supply of P was a controlling strategy for stable operation.
The effect of phosphate concentration on the anammox-HAP process was investigated in this work. A high total nitrogen removal efficiency (>82.6%) and a stable total phosphate removal efficiency (>56.2%) was achieved in reactor with the phosphate concentration over 11.4 mg L−1. However, a phosphate concentration below to 5.7 mg L−1, a floatation of sludge occurred caused the deterioration of process. A new understanding for the floatation was divided into three stages: the stable stage, bulking stage and floating stage. First, anammox biofilm coupled with HAP for granulation in the stable stage. Second, the aggregation of bulking sludge resulted in changes in viscoelastic properties of the sludge. Third, the floatation resulted from unreleasable gas bubbles in the granules wrapped a high concentrations of slime layer proteins. Overall, this paper suggests that a control strategy was a sufficient supply of phosphate for the stable operation.
•Causality test was used to identify directional controls on EF variability.•Rn was mainly allocated to H and daily EF was averaged at 0.14.•The impacts of Ta and Rn on EF were substantial in the ...coastal wetland.•Dominant control of RH on EF was detected with the prevailing onshore winds.•Poor vegetation status, affected by salinity and flood, limited EF variability.
Elucidating environmental controls on land surface energy partitioning at ecosystem levels is critical for better understanding water and energy cycles across landscapes; however, the underlying effects of changing atmospheric, soil, and vegetation conditions on the energy partitioning in coastal wetlands are not well understood. Here, the temporal variations in surface evaporative fraction (EF; defined as latent heat flux-LE divided by the sum of LE and sensible heat flux-H) and its responses to environmental conditions were analyzed at half-hourly and daily timescales, using measurements from a Bowen ratio tower situated in an herbaceous coastal wetland in Tianjin, Northern China. Results showed that net radiation (Rn) was mainly allocated to H with an average H/Rn of 0.90 and daily EF was averaged at 0.14 during the study period. The EF patterns in the studied coastal wetland were significantly different from those in terrestrial ecosystems, which was mainly attributed to the complex interactions in local atmospheric, soil, and vegetation conditions. Specifically, significant directional relationships among environmental variables were detected through the Granger causality analysis (GCA), especially at half-hourly timescales. The GCA and boosted regression tree methods showed that energy-related factors (i.e., air temperature and Rn) were the dominant controls on EF. Poor vegetation status, which was affected by salinity and flood stress, primarily limited LE and subsequently temporal EF variability. During the wet period, atmospheric conditions changed with the prevailing onshore winds, resulting in the dominant control of relative humidity on EF variations. Overall, the EF variability in coastal wetlands was not solely controlled by energy but was more tightly constrained by atmospheric conditions and vegetation dynamics, which offers new insights into energy exchanges in coastal wetland ecosystems, especially for determining the coupling strength between atmosphere and land surface processes.
•Granules of various sizes achieved N and P removal with excellent settleability.•Biomineralization-based pattern achieves granulation.•Poly-pellet HAP skeletons attached by anammox ...biofilms.•Three-layered granules were formed based on biomineralization.•Granulation cycle mechanism was revealed for the growth and regeneration of granules.
The formation of anammox-hydroxyapatite (HAP) coupled granules has been shown to be an approach to efficient nitrogen removal and phosphorus recovery in the anammox EGSB reactor. However, the granulation cycle mechanism of anammox-HAP coupled granules for sustainable regeneration and growth is still not well understood. In this study, the microstructure, chemical composition and microbial structure of a total of six different-sized granules, from 0.25 mm to 2.8 mm, was determined. An SEM-EDS analysis indicated that the small granules (<0.5 mm) were composed of poly-pellet clusters with anammox biofilms attached to the HAP cores, and the large granules (>0.5 mm) consisted of a three-layer structure: a surface anammox biofilm layer, a middle connection layer, and a HAP mineral inner core. The analysis of elemental composition and microbial structure suggested homogenous granular characteristics regardless of granule size. The dominant microorganisms were anammox bacteria of Candidatus Kuenenia stuttgartiensis and heterotrophic denitrifying bacteria. Based on these results, a granulation cycle mechanism for anammox-HAP coupled granules was proposed for the first time. The growth of the small granules with the simultaneous enlargement of anammox biofilms and HAP cores results in the formation of large granules. Large granules regenerate new small granules in a two-step procedure. The first step is the separation of embryo HAP crystals from the mother core via heterogeneous growth, and the second step is the separation of the biofilms due to biodegradation and shear stress.
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•Biochar aging declines ameliorating effect of biochar on soil acidity in short-term.•Effects of incubation conditions on soil acidity amendment using biochar are few.•Local forestry wastes biochar ...can be used to amend soil acidity in study region.
Biochar has positive effects as a soil acidity amendment which is a global concern. However, few studies have been reported on the effect of aged biochar on soil acidity. Incubation methods with different ventilation conditions may induce different effects on soil acidity amendment using biochar. This study analyzed the effects of fresh and aged biochars on soil acidity amendment with different incubation methods. Samples of typical acidic soil (plinthudults) and fresh Pinus massoniana bark were collected from the hilly red soil region of southern China and used to create biochar (PB) with the oxygen-limited pyrolysis method at 450°C. A 4-month-aged PB (PBa) which was produced by a natural forest fire was collected from the same area as that of biochar PB. A 69 days incubation experiment was conducted using an improved incubation method. The treatments comprised 100g soil+2g PBa (PBA), 100g soil+2g PB (ventilated incubation, PBV), 100g soil+2g PB (sealed incubation, PBS) and 100g soil only incubated under ventilated (CKV) and sealed (CKS) conditions. Soil pH was measured periodically. Soil exchangeable base cations, exchangeable acidity, exchangeable aluminum (Al3+) and cation exchange capacity (CEC) were measured after incubation. Throughout the incubation period, PB and PBa positively enhanced soil pH (P<0.05), with PB exhibiting more remarkable effects. A similar effect was also observed for soil exchangeable Al3+ and exchangeable acidity. After incubation, soil pH values of PBV (5.05±0.02) and PBS (4.99±0.03) were than the value of PBA (4.98±0.03), with nonsignificant differences (P>0.05) between values in PBV and PBS. PB addition improved soil exchangeable base cations and base saturation compared to PBa addition. Soil CEC levels in PBA, PBV, and PBS were not significantly different from those in CKV and CKS, but CEC in PBV and PBS were significantly higher than the CEC in PBA. All parameters in PBV were not significantly different from the parameters in PBS. Biochar PB can be used to amend soil acidity, but the efficiency declines to a certain extent if biochar PB has undergone a short-term aging before being added to soils. The different ventilation conditions had little influence on soil acidity amendment using biochar.
The complete methanogenic degradation of N, N-dimethylformamide (DMF) was achieved in this study. Initially, DMF was found to be feebly degradable by a lab-scale submerged anaerobic membrane ...bioreactor (SAnMBR) using normal anaerobic digestion sludge (ADS) even after 120-day's culturing. However, aerobic DMF-degrading activated sludge (AS) was rapidly cultivated in a continuous aeration reactor (CAR). A specially designed anaerobic co-cultured sludge (ACS) made by artificially mixing AS with ADS was successfully domesticated by a long term repeated batch experiment. The results demonstrated that ACS could effectively degrade over 5000 mg L−1 DMF for methane recovery. The metabolic pathway and stoichiometric equation of DMF methanogenic degradation were also revealed and verified in detail. It was confirmed that under the anaerobic condition, with the help of enzyme, DMF converts into dimethylamine and formic acid, and the intermediates are effectively fermented through methylotrophic/hydrogenotrophic methanogenesis. Analysis of the microbial community suggested that some facultatively anaerobic bacteria played the key roles in methanogenic degradation due to their DMF-hydrolyzing ability. By co-culturing two sources of inoculum under the anaerobic condition, the symbiosis of facultatively anaerobic DMF-hydrolyzing bacteria and methylotrophic/hydrogenotrophic methanogens makes methanogenic degradation of DMF available. This study also provides a novel sludge cultivation method for anaerobic treatment of degradation-resistant organics.
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•Weak biodegradability of DMF was observed under the anaerobic condition.•Anaerobic degradation of DMF could be achieved by a mixed consortium.•Stoichiometric equation of DMF anaerobic degradation was verified.•DMF-hydrolyzing anaerobes and enzyme make DMF degradable anaerobically.•Intermediates of DMF follow methylotrophic/hydrogenotrophic metabolisms.
•A concept of AnMBR-PN/A process was proposed for mainstream treatment.•In-situ FA/FNA exposure eliminated Nitrospira while retained Nitosonomas community.••DO limitation prevented switch of the NOB ...community in the mainstream conditions.•The effluent TN of the mainstream PN/A system was lower than 10 mg-N/L.•Enhanced hydrodynamic shear force resulted in sludge settleability deterioration.
In this pilot-scale study, an innovative mainstream treatment process that couples the anaerobic membrane reactor (AnMBR) with a one-stage PN/A system was proposed for advancing the concept of carbon neutrality in the municipal wastewater treatment plant. This work demonstrates the start-up procedure of a pilot-scale one-stage PN/A system for mainstream treatment. The 255-day start-up of the one-stage PN/A system involved the cultivation of ammonium-oxidizing bacteria (AOB) from the activated sludge, suppression of nitrite-oxidizing bacteria (NOB), investigation of in-situ growth kinetics of anammox bacteria (AnAOB), and the 50-day operation of the pilot-scale AnMBR-PN/A process for natural mainstream treatment. It is verified in the pilot-scale system for the first time that the in-situ free ammonia (FA) and free nitrous acid (FNA) exposure could effectively eliminate the Nitrospira (the NOB genus) while retaining the Nitosonomas (the AOB genus) community in the suspended sludge. NOB community rebounding was not detected even at the mainstream conditions with low nitrogen concentrations (Influent ammonium concentration=38±6 mg-NH4+-N/L) by intermittent aeration to control the system dissolved oxygen (DO) below 0.5 mg/L. The results of the mainstream treatment showed that the average effluent total nitrogen (TN) in the coupled process was generally lower than 10 mg-N/L, which meets the discharge limits of most prefectures in Japan. The investigated results of the in-situ anammox bacteria (AnAOB) growth kinetics suggested that the promoted start-up strategy of taking advantage of the warm months with higher mainstream temperature to achieve the rapid in-situ growth of the AnAOB is applicable in the investigated regions. From the perspective of the removal performance of the TN and organic substance, the AnMBR-PN/A process has great potential as the layouts of the carbon-neutral mainstream wastewater treatment plants.
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•High COD, TP and TN removal were available in biofilters coordinately.•Sulfur has faster denitrifying rate but lowers pH and produces more sulfate.•Pyrite is more potential and ...feasible if strict condition can be ensured.•S-oxidizing bacteria simplify diversity of S-biofilter and acidize environment.•Mixotrophic process in P-biofilter improves diversity but removal is unstable.
Two parallel biofilters applying sulfur/pyrite-based autotrophic denitrification were investigated for removing COD, TP and TN by a coordinated process. Results demonstrated good performance by removing 86.32% vs 87.14% COD and 92.56% vs 89.65% NH4+-N. Biofilter with sulfur (BS) was superior on nitrate (89.74% vs 80.72%) and TN removal (83.18% vs 70.42%) while biofilter with pyrite (BP) was better on TP removal (82.58% vs 77.40%) and maintaining sulfate (27.56mgL−1 vs 41.55mgL−1) and pH (7.13 vs 6.31). Water-permeable adsorbents lowered clogging risk and buffered loading. Clone library revealed reasons of diversities, pH variation and sulfate accumulation of both biofilters. Sulfur was efficient on denitrification but whose byproducts were troublesome, pyrite produced less byproduct but which was sensitive to organics. This research was the first attempt to systematically compare two promising alternatives and their merits/demerits for rural wastewater on-site treatment.
