Co-precipitation of heavy metals with struvite from digested swine wastewater: Role of suspended solids.

Struvite production can recover ammonia and phosphorous from digested wastewater as fertilizer. During struvite generation, most of the heavy metals was co-precipitated with ammonia and phosphorous into struvite. Understanding the precipitation behavior of heavy metals with suspended solids (SS) might provide the possible strategy for the control of co-precipitation. In this study, the distribution of heavy metals in SS and their role on the co-precipitation during struvite recovery from digested swine wastewater were investigated. The results showed that the concentration of heavy metal (including Mn, Zn, Cu, Ni, Cr, Pb and As) ranged from 0.05 to 17.05 mg/L in the digested swine wastewater. The distribution analysis showed that SS with particles > 50 µm harbored most of individual heavy metal (41.3-55.6%), followed by particles 0.45-50 µm (20.9-43.3%), and SS-removed filtrate (5.2-32.9%). During struvite generation, 56.9-80.3% of individual heavy metal was co-precipitated into struvite. The contributions of SS with particles > 50 µm, 0.45-50 µm, and SS-removed filtrate on the individual heavy metal co-precipitation were 40.9-64.3%, 25.3-48.3% and 1.9-22.9%, respectively. These finding provides potential way for controlling the co-precipitation of heavy metals in struvite.

Distribution of extracellular amino acids and their potential functions in microbial cross-feeding in anaerobic digestion systems.

Anaerobic digestion is a prevalent bioenergy production process relying on a complex network of symbiotic interactions, where the nutrient based cross-feeding is an essential microbial mechanism. Here, the cross-feeding function was assessed by analyzing extracellular polymeric substances-associated amino acids in microbial aggregates collected from 14 lab-scale anaerobic digesters, as well as deciphering their genetically biosynthetic potential by syntrophic bacteria and methanogens. The total concentration of essential amino acids ranged from 1.2 mg/g VSS to 174.0 mg/g VSS. The percentages of glutamic acid (8.5 âˆ¼ 37.6%), lysine (2.7 âˆ¼ 22.6%), alanine (5.6 âˆ¼ 13.2%), and valine (3.0 âˆ¼ 10.4%) to the total amount of detected amino acids were the highest in most samples. Through metagenomics analysis, several investigated syntrophs (i.e., Smithella, Syntrophobacter, Syntrophomonas, and Mesotoga) and methanogens (i.e., Methanothrix and Methanosarcina) were auxotrophies, but the genetic ability of syntrophs and methanogens to synthesize some essential amino acids could be complementary, implying potential cross-feeding partnership.

Inhibition mitigation and ecological mechanism of mesophilic methanogenesis triggered by supplement of ferroferric oxide in sulfate-containing systems.

Methanogenesis can be inhibited by volatile fatty acids (VFAs) accumulation and sulfate during anaerobic wastewater treatment. In this study, effects of ferroferric oxide (Fe3O4) on VFAs degradation and methanogenesis in sulfate-containing environment were investigated. Methanogenesis in reactors with or without sulfate were both favored through the addition of Fe3O4. In reactors without sulfate, the dosage of Fe3O4 increased the maximum methane production rate by 21.7% accompanied with faster acetate and propionate degradation. Metagenomic analysis showed that Fe3O4 mainly promoted electron exchange between Mesotoga, Syntrophobacter, Smithella and Methanosaeta without altering the syntrophic patterns. However, in the sulfate-containing reactor with low methanogenic efficiency, syntrophic ethanol users and Methanosaeta were replaced by sulfate-reducing bacteria and Methanosarcina, respectively. The supplement of Fe3O4 re-enriched the syntrophic partners inhibited by sulfate and rebuilt a new syntrophic interaction with high efficiency similar to that in sulfate-free environment, leading to better methanogenic performance in sulfate-containing environment.

Comprehensive assessment of system performance in a full-scale wastewater treatment plant with an anaerobic/anoxic/aerobic membrane bioreactor combined with the ozonation process.

The system performance, economic cost and environmental impact of a full-scale anaerobic/anoxic/aerobic/membrane bioreactor (3AMBR) combined with the ozonation process were evaluated. The 3AMBR/ozonation process removed biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, NH4-N and total phosphorus efficiently, with removal percentages above 94%, while the total nitrogen removal percentage was only 70%. The multiple linear regression analysis showed that hydraulic retention time (HRT) had a significant effect on nitrogen removal. A low HRT benefited nitrogen removal. Ferrous sulfate dosage close to the optimal value and a high mixed liquid suspended solid could enhance the phosphorus removal. The electricity cost accounted for 88% of the total economic costs. Greenhouse gas (GHG) emissions from the BOD oxidation and endogenous decay accounted for more than 50% of total emissions. The second largest GHG emission source was electricity consumption, accounting for 41%. The key to reduce the eutrophication was to enhance nitrogen removal. The composite cost of the 3AMBR/ozonation process was 251 CNY/t CODeq removed, among which economic cost accounted for 82.5%, while environmental impact cost accounted for a small proportion.

Enhanced growth and fatty acid accumulation of microalgae Scenedesmus sp. LX1 by two types of auxin.

Microalgae are potential candidates for the production of valuable products, such as renewable biodiesel, health products and pigments. However, low biomass productivity has restricted their large-scale applications. In this study, the effects of two auxins (one natural type of indole-3-acetic acid (IAA) and the other synthetic type of 2,4-dichlorophenoxyacetic acid (2,4-D)) on the growth and fatty acid methyl esters (FAMEs) production of a freshwater microalgae Scenedesmus sp. LX1 were investigated. Both auxins showed a "low dosage-promotion and high dosage-inhibition" effect on the growth and FAMEs accumulation. The optimum dosage of IAA and 2,4-D were 1mgL-1 and 0.1mgL-1, respectively. Moreover, the IAA could increase the monounsaturated fatty acid content. The auxins may promote the growth by enhancing the photosynthetic activity through increasing chlorophyll contents. Therefore, auxin significantly enhanced microalgal growth and FAMEs accumulation, and has a potential for application in developing efficient microalgal cultivation.

Removal of nitrogen and phosphorus from the secondary effluent in tertiary denitrifying biofilters combined with micro-coagulation.

Effective control of nitrogen and phosphorus in secondary effluent can reduce or avoid the eutrophication of receiving water bodies. Two denitrifying biofilters (DNBFs) packed with different sizes of quartz sands combined with micro-coagulation were operated for simultaneous removal of nitrogen and phosphorus from the secondary effluent. The quartz sand size in one DNBF was 2-4 mm (DNBFS), and in the other was 4-6 mm (DNBFL). In both DNBFs, methanol was used as the electron donor and different organic carbon to nitrogen (C/N) ratios were applied. Under C/N ratios of 1.5, 1.25, and 0.75 g/g, the nitrate nitrogen (NO3(-)-N) removal percentages were 73%, 77%, and 50% in DNBFS, and 43%, 25%, and 21% in DNBFL; the effluent total phosphorus concentrations were 0.15, 0.14, and 0.18 mg/L in DNBFS, and 0.29, 0.35, and 0.24 mg/L in DNBFL. The performance of both biofilters was quite stable within a backwashing cycle. The NO3(-)-N reduction rates were 1.31, 1.10, and 0.48 mg/(L·min) in DNBFS, and 0.97, 0.27, and 0.10 mg/(L·min) in DNBFL. For biomass detached from both biofilters, their denitrifying activities were similar. Biofilm biomass in DNBFS was higher than that in DNBFL, inducing a high denitrification efficiency in DNBFS.

Effects of sludge retention times on nutrient removal and nitrous oxide emission in biological nutrient removal processes.

Sludge retention time (SRT) is an important factor affecting not only the performance of the nutrient removal and sludge characteristics, but also the production of secondary pollutants such as nitrous oxide (N2O) in biological nutrient removal (BNR) processes. Four laboratory-scale sequencing batch reactors (SBRs), namely, SBR5, SBR10, SBR20 and SBR40 with the SRT of 5 d, 10 d, 20 d and 40 d, respectively, were operated to examine effects of SRT on nutrient removal, activated sludge characteristics and N2O emissions. The removal of chemical oxygen demand or total phosphorus was similar under SRTs of 5-40 d, SRT mainly affected the nitrogen removal and the optimal SRT for BNR was 20 d. The molecular weight distribution of the effluent organic matters was in the range of 500-3,000 Da under SRTs of 5-40 d. The lowest concentration of the effluent soluble microbial products concentration was obtained at the SRT of 5 d. Nitrifier growth was limited at a short SRT and nitrite existed in the effluent of SBR5. With increasing SRTs, mixed liquor suspended solids concentration increased while the excess sludge production was reduced due to the high endogenous decay rate at high SRTs. Endogenous decay coefficients were 0.020 d⁻¹, 0.036 d⁻¹, 0.037 d⁻¹ and 0.039 d⁻¹ under SRTs of 5-40 d, respectively. In BNR, the N2O emission occurred mainly during the aerobic phase and its emission ratio decreased with increasing SRTs. The ratio between the N2O-N emission and the removed ammonium nitrogen in the aerobic phase was 5%, 3%, 1.8% and 0.8% at the SRT of 5 d, 10 d, 20 d and 40 d, respectively. With low concentrations of dissolved oxygen and high concentrations of oxidized nitrogen, the N2O emission was significantly accelerated due to heterotrophic denitrification activities.

Dynamics of intracellular polymers in enhanced biological phosphorus removal processes under different organic carbon concentrations.

Enhanced biological phosphorus removal (EBPR) may deteriorate or fail during low organic carbon loading periods. Polyphosphate accumulating organisms (PAOs) in EBPR were acclimated under both high and low organic carbon conditions, and then dynamics of polymers in typical cycles, anaerobic conditions with excess organic carbons, and endogenous respiration conditions were examined. After long-term acclimation, it was found that organic loading rates did not affect the yield of PAOs and the applied low organic carbon concentrations were advantageous for the enrichment of PAOs. A low influent organic carbon concentration induced a high production of extracellular carbohydrate. During both anaerobic and aerobic endogenous respirations, when glycogen decreased to around 80 ± 10 mg C per gram of volatile suspended solids, PAOs began to utilize polyphosphate significantly. Regressed by the first-order reaction model, glycogen possessed the highest degradation rate and then was followed by polyphosphate, while biomass decay had the lowest degradation rate.

Partial nitrification and nutrient removal in intermittently aerated sequencing batch reactors treating separated digestate liquid after anaerobic digestion of pig manure.

The performance of an intermittently aerated sequencing batch reactor (IASBR) technology was investigated in achieving partial nitrification, organic matter removal and nitrogen removal from separated digestate liquid after anaerobic digestion of pig manure. The wastewater had chemical oxygen demand (COD) concentrations of 11,540 ± 860 mg/L, 5-day biochemical oxygen demand (BOD(5)) concentrations of 2,900 ± 200 mg/L and total nitrogen (TN) concentrations of 4,041 ± 59 mg/L, with low COD:N ratios (2.9) and BOD(5):COD ratios (0.25). Synthetic wastewater, simulating the separated digestate liquid with similar COD and nitrogen concentrations but BOD(5) of 11,500 ± 100 mg/L, was also treated using the IASBR technology. At a mean organic loading rate of 1.15 kg COD/(m(3) d) and a nitrogen loading rate of 0.38 kg N/(m(3) d), the COD removal efficiency was 89.8% in the IASBR (IASBR-1) treating digestate liquid and 99% in the IASBR (IASBR-2) treating synthetic wastewater. The IASBR-1 effluent COD was mainly due to inert organic matter and can be further reduced to less than 40 mg/L through coagulation. The partial nitrification efficiency of 71-79% was achieved in the two IASBRs and one cause for the stable long-term partial nitrification was the intermittent aeration strategy. Nitrogen removal efficiencies were 76.5 and 97% in IASBR-1 and IASBR-2, respectively. The high nitrogen removal efficiencies show that the IASBR technology is a promising technology for nitrogen removal from low COD:N ratio wastewaters. The nitrogen balance analysis shows that 59.4 and 74.3% of nitrogen removed was via heterotrophic denitrification in the non-aeration periods in IASBR-1 and IASBR-2, respectively.

Inhibitory effect of copper on enhanced biological phosphorus removal.

Copper inhibition of enhanced biological phosphorus removal (EBPR) was examined in batch experiments under anaerobic and aerobic conditions. Inhibition was represented by both acetate uptake and phosphorus release coefficients under anaerobic conditions, and by a phosphorus uptake coefficient under aerobic conditions. The results showed that copper inhibition of EBPR occurred mainly during aerobic phosphorus uptake and a first-order phosphorus uptake coefficient can be better used to describe the inhibition effect. For the aerobic phosphorus uptake using the EBPR activated sludge, (i) copper inhibition started at 0.07 mg/l, (ii) 50% and 100% inhibition occurred at 0.30 mg/l and 0.53 mg/l, respectively, and (iii) the inhibition constant was 0.48 mg/l.

Production of polyhydroxybutyrate by activated sludge performing enhanced biological phosphorus removal.

In this study, polyhydroxybutyrate (PHB)--a biodegradable plastics material--was produced by activated sludge performing enhanced biological phosphorus removal (EBPR) in batch experiments under anaerobic, aerobic and anaerobic/aerobic conditions. Under anaerobic conditions, the maximum PHB content of the dry biomass was 28.8% by weight, while under aerobic or anaerobic/aerobic conditions, the maximum PHB content was about 50%. The PHB production rate with respect to the volatile suspended solids (VSS) was: (i) 70 mg/(g VSS)h under aerobic conditions that followed anaerobic conditions, (ii) 156 mg/(g VSS)h under anaerobic condition, and (iii) 200mg/(g VSS)h under aerobic conditions with energy also supplied from polyphosphate. A side stream, with initially anaerobic conditions for PHB accumulation and phosphorus release, and then aerobic conditions for PHB accumulation, was proposed. In this side stream, biomass with a high PHB content and a high PHB production rate could be both achieved.

Microbial community associated with glucose-induced enhanced biological phosphorus removal.

The microbial community associated with enhanced biological phosphorus removal with glucose as the main carbon source at 11 degrees C was investigated using microscopy and molecular fingerprinting techniques. The study lasted 77 days and comprised two stages-Stage 1 when the mixture of glucose, yeast and dried milk was the organic carbon source and Stage 2 when glucose was the single carbon source. Rhodocyclus-related polyphosphate accumulating organisms, alpha-Proteobacteria and Bacteroidetes constituted 42% in Stage 1 and 45% in Stage 2, 21% in Stage 1 and 16% in Stage 2, and 10% in Stage 1 and 7% in Stage 2 of the total bacteria, respectively. The Trichococcus genus from the low GC Gram-positive bacteria was possibly responsible for lactic acid production from glucose. The microbial community was gradually changing throughout the experiment and appeared to stabilize towards the end of the experiment. Periods of suboptimal phosphorus removal could have been caused by competition among different microbial communities for carbon substrate.

Nitrogen and phosphorus removal from domestic strength synthetic wastewater using an alternating pumped flow sequencing batch biofilm reactor.

Nutrient removal from domestic strength synthetic wastewater by an alternating pumped flow sequencing batch biofilm reactor (APFSBBR) was investigated in this laboratory study. The APFSBBR comprised two reactor tanks (Reactors 1 and 2) with two identical biofilm modules of vertical tubular plastic media with a high specific surface area, one in each tank. The APFSBBR was operated in cycles of four phases: fill, anaerobic, aerobic, and draw. During the fill phase, Reactor 1 was half-filled with domestic strength synthetic wastewater. During the subsequent anaerobic phase, most of the phosphorus release took place from the submerged biofilm in this reactor. In the aerobic phase, the wastewater was circulated by pumps between Reactors 1 and 2, resulting in denitrification at the start of the aerobic phase due to low oxygen concentrations, followed by nitrification and luxury uptake of phosphorus when oxygen concentrations increased. During the draw phase, Reactor 2 was half-emptied of the treated water. At the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) loading rates on the total biofilm area of 3.20 g COD, 0.33 g TN, and 0.06 g TP m(-2) d(-1), the removal efficiencies were 97, 85, and 92% for COD, TN, and TP, respectively.