Short-time aerobic digestion (STAD) of sludge requires low investment and has the advantages of short sludge retention time and rapid degradation of organic matter in waste activated sludge (WAS). ...This research conducted STAD at three temperature gradients (15 °C, 25 °C, and 35 °C). Characteristics of EPS and microbial community structure of raw and fermented sludge were analyzed, and environmental application potential of STAD at different temperatures was explored. STAD treatment improved both polysaccharide (PS) and protein (PN) contents in EPS, with increases of 5.7–18.35 % and 20.98–28.57 %, respectively. Aromatic protein-like substances (Peak E) and tryptophan protein substances (Peak F) were main components of PN in EPS. The microbial species richness decreased as the STAD temperature increased. At the class level, STAD temperature significantly affected Alphaproteobacteria, Gemm-1, Chloracidobacteria, Acidimicrobiia, Ellin6529, Betaproteobacteria, and SJA-28. From an application perspective, the specific resistance to filtration (SRF) value of WAS after STAD treatment at 35 °C was decreased to 7.01 × 107 m/kg with a 17.34 % reduction, indicating improvement in the dewaterability of the sludge. The Pb2+ adsorption efficiency per unit volume of EPS increased by 10.0–16.2 % after STAD treatment of WAS at different temperatures for 4 h. This research elucidated the impact of temperature on WAS in STAD systems, finding that microbial abundance correlated with EPS characteristics. The research results provide a basis for optimizing the system temperatures in STAD systems and a deeper understanding of the benefits of STAD in practical applications for sludge resource utilization.
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•At phyla/class level, eleven bacteria were significantly related to STAD temperature.•The content of PN (20.98%–28.57 %) and PS (5.70%–18.35 %) in EPS improved by STAD treatment.•The SRF of sludge was reduced by 17.34 % after STAD treatment at 35 °C.•The Pb2+ adsorption efficiency of per unit volume EPS improved 10.01%–16.2 %.
Due to its high toxicity, persistence, and bioaccumulation in the food chain, controlling cadmium (Cd) pollution in wastewater is urgent. Activated carbon is a popular material for removing Cd. To ...improve the Cd(II) adsorption efficiency by increasing the number of oxygen-containing functional groups, Phragmites australis-activated carbon (PAAC) was modified with mannitol at a low temperature (150 °C). The textural and chemical characteristics of PAAC and modified PAAC (M-PAAC) were analyzed by surface area analysis, elemental analysis, Boehm’s titration, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Batch adsorption experiments were conducted to investigate the influence of Cd(II) concentration, contact time, ionic strength, and pH on Cd(II) adsorption. The main adsorption mechanisms of Cd(II) on activated carbon were quantitatively calculated. The results showed that mannitol modification slightly decreased the S BET (5.30% of PAAC) and increased the content of carboxyl, lactone, and phenolic groups (total increase of 43.96% with PAAC), which enhanced the adsorption capacity of PAAC by 58.59%. The adsorption isotherms of PAAC and M-PAAC were described well using the Temkin model, while the intraparticle diffusion model fitted the Cd(II) adsorption kinetics best. Precipitation with minerals was a crucial factor for Cd(II) adsorption on activated carbon (50.40% for PAAC and 40.41% for M-PAAC). Meanwhile, the Cd(II) adsorption by M-PAAC was also dominated by complexation with oxygen-containing functional groups (33.60%). This research provides a method for recovering wetland plant biomass to prepare activated carbon and efficiently treat Cd-containing wastewater.
In the actual water environment, the health risk of waterborne viruses is evaluated to be 101–104 times higher at a similar level of exposure compared with bacteria and has aroused strong concern in ...many countries in the world. Photocatalytic membrane reactor (PMR), a new process for virus inactivation in water, has gradually become one of the main tools to inactivate pathogenic organisms in water. However, there is relatively little attention to the effect of natural organic matters (NOMs) on the PMR system, which actually exists in the water environment. In this paper, the TiO2-P25, a common type in sales and marketing, was selected as the photocatalyst, and humic acid was regarded as the representative substance of NOMs for investigating thoroughly the influence of humic acid on virus removal by the PMR system. It was found that competitive adsorption between the virus and humic acid occurred, which markedly reduced the amount of virus adsorbed on the surface of the photocatalyst. Moreover, with humic acid, the direct contact behavior between the virus and the photocatalyst was blocked to some extent, and the disinfection of phage f2 by the active free radicals produced by photocatalysis was furthermore badly affected. Meanwhile, the special structure of humic acid, which made humic acid be able to absorb light of 270–500 nm, led to the reduction of photocatalytic efficiency. Further experiments showed that when there was a certain concentration of humic acid in water, intermittent operation mode or higher membrane flux (>40 L/(m2·h)) was selected to partly alleviate the adverse effects of humic acid.
Successive systems using yeast and activated sludge (AS) were developed to treat monosodium glutamate manufacturing wastewater (MSGW). The yeast system allowed over 80% removal of chemical oxygen ...demand (COD) and a rise of pH from 2.5 to 6.5 on treating MSGW directly (COD 25,000
mg/l and NH
4
+–N 19,000
mg/l). Observation of the microbial community using a scanning electron microscope indicated that the two species of yeast (
Candida halophila and
Rhodotorula glutinis) were predominant in the biofilm reactor during 2 months of operation. The suspended solids (SS) of effluents from the yeast reactor were mainly composed of yeasts and fermentative bacteria used in glutamate production. This part of SS contained 55.8% protein and 18 amino acids and could be utilized as a source of single cell protein (SCP) as animal food additive. The effluent from the yeast system was fed into the activated sludge system after NH
4
+–N was reduced to a level of 1000
mg/l through air stripping. The activated sludge system could remove 50–70% of the remaining COD further, and the effluent COD and SS were constantly below 1300 and 70
mg/l, respectively. The combined system biologically removed about 95% COD from MSGW, and the COD could be further reduced to below 360
mg/l with coagulation under an FeCl
3 dose of 1400
mg/Fe l.
Ten yeast strains acquired from different sources and capable of utilizing vegetable oil or related compounds (fatty acid or oleic acid) as sole carbon sources were inoculated into a sequencing batch ...reactor (SBR) for the treatment of high-strength vegetable oil-containing wastewater. The SBR system stably removed >89% of chemical oxygen demand (COD) and >99% of oil when fed with wastewater containing 15 g/L COD and 10 g/L oil in average. Denaturing gradient gel electrophoresis of polymerase chain reaction-amplified 26S rRNA genes showed that among the ten yeast strains, only
Candida lipolytica
,
Candida tropicalis
, and
Candida halophila
were dominant in the system. To elucidate the major factors affecting the selection of yeast strains in the SBR system, the three dominant strains were compared with two non-dominant strains in terms of COD removal performance, biomass yield, cell settleability, cell flocculation ability, cell emulsification ability, and surface hydrophobicity. Results showed that hydrophobicity and emulsification ability of yeast cells were the two most important factors determining the selection of yeast strains in the treatment of high-strength oil-containing wastewater.
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•Yeast degraded PN, PS, amino acids, and fluorescent components in EPS.•Yeast transformed macromolecular organics to small molecular ones in EPS.•Addition of 0.75 g/L of yeast ...enhanced the dewaterability of AS.•Yeast reduced hydrophilic organics or functional groups in EPS.•Yeast enhanced the AS dewaterability and reduced the in-situ biomass in SBR.
Candida Tropicalis was used to improve the dewaterability of activated sludge (AS) and reduce its biomass by degrading EPS in AS. The protein, polysaccharide, and hydrophilic amino acids in EPS decreased by 54.50, 29.20, and 61.01%, respectively. Meanwhile, molecular weight distribution indicated that yeast degraded macromolecular organics into small molecular ones. The direct addition of yeast to AS was more conducive to EPS degradation. With the addition of 0.75 g/L of wet yeast cells and 24 h of aeration enhanced the dewaterability of AS. The CST and MLSS decreased by 24.44 and 10.51%, respectively. After 30 days of operation of lab-scale continuous SBRs, the CST and MLSS of AS were reduced by 6.37 ± 2.01 and 3.57 ± 0.52%, respectively. FTIR spectroscopy results showed that some hydrophilic functional groups were reduced. This study provides a new approach for the in-situ reduction of AS in wastewater treatment plant.
The performance, microbial enzymatic activities and the microbial community of sequencing batch reactors (SBRs) were evaluated under the single and combined nickel (Ni2+) at 20 mg/L and cadmium ...(Cd2+) at 10 mg/L. The single and combined Ni2+ and Cd2+ had no adverse impacts on the COD removal, whereas the NH4+-N removal efficiency declined sharply from about 99% to 34.42% and 42.67% under the single Ni2+ and combined Ni2+ and Cd2+. Compared with the absence of Ni2+ or Cd2+, the specific oxygen uptake rate (SOUR), ammonia-oxidizing rate (SAOR), nitrite-oxidizing rate (SNOR), nitrite-reducing rate (SNIRR) and nitrate-reducing rate (SNRR) declined by 24.09%, 56.63%, 51.50%, 58.01% and 52.09% under the combined Ni2+ and Cd2+, which were slower than the sum of those under single Ni2+ and Cd2+. The dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrate reductase and nitrite reductase activities showed the similar varying trends to the SOUR, SAOR, SNOR, SNIRR and SNRR, suggesting that the combined Ni2+ and Cd2+ displayed antagonistic inhibition on the nitrogen removal rates and microbial enzyme activities. The combined Ni2+ and Cd2+ declined the microbial diversity and richness less than the sum of those under single Ni2+ and Cd2+. The relative abundance of Nitrosomonas, Nitrospira and identified denitrifying bacteria displayed some changes under single and combined Ni2+ and Cd2+. These findings would contribute to better understand the combined impacts of multiple heavy metals on biological wastewater treatment systems.
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•Combined Ni2+ and Cd2+ showed less inhibition on nitrogen removal than Ni2+ and Cd2+.•Combined Ni2+ and Cd2+ inhibited the nitrogen removal rate less than Ni2+ and Cd2+.•Combined Ni2+ and Cd2+ displayed antagonistic inhibition on the enzymatic activity.•Combined Ni2+ and Cd2+ showed less inhibition on microbial diversity and richness.
Extracellular polymeric substances (EPS) extracted from waste-activated sludge (WAS) have the potential to remove heavy metal ions from wastewater; both the spatial distribution and metal adsorption ...of EPS from WAS after nitrogen aeration were systematically investigated in this study. Compared with air aeration, nitrogen aeration significantly improved the contents of proteins (PN) and polysaccharides (PS) in the Slime-EPS (S-EPS) and loosely-bound EPS (LB-EPS), significantly increased the PS content, and slightly increased the PN content in the tightly-bound EPS (TB-EPS). The variations in the fluorescence intensities (FI) of the peaks I and II for the S-EPS, LB-EPS and TB-EPS were basically consistent with the abovementioned variations in the concentrations of these EPS. Notably, nitrogen aeration dramatically improved the content of protein-like substances in the LB-EPS. For the same aeration time, the Pb
2+
reclamation rates obtained by the LB-EPS extracted from the nitrogen-aerated WAS were much higher than those achieved by the LB-EPS extracted from the air-aerated WAS. The FTIR analyses further indicated that nitrogen aeration improved the contents of the functional groups, especially -OH, -COOH and -NH
2
, responsible for binding heavy metals, in both the LB-EPS and TB-EPS. The SEM analyses verified that the nitrogen scours contributed to the EPS release, and Pb
2+
reclamation was achieved
via
the attachment of Pb
2+
onto the edge of the EPS. The influences of the nitrogen aeration on the spatial distribution and metal adsorption of the EPS in WAS were revealed for the first time in this study. Thus, this study lays the foundation for the application of nitrogen aeration in the resource utilization of WAS.
Nitrogen aeration was superior to air aeration because of the higher EPS production and Pb
2+
adsorption in the utilization of WAS.
Resource recovery of the slurry in septic tanks around the cities should be a promising and sustainable approach. However, the amorphous form of the slurry and safety of use put a big challenge on ...land use of the wastes. This study aimed to transform the slurry into sanitary, nutrient-rich granules and assess the environmental and health risks from land use in agriculture. The granules' impact on soil fertility, plant growth, heavy metal accumulation, pathogenic bacteria and soil bacterial communities was evaluated in field experiments with radish as a test crop. The granules were found to be rich in essential nutrients and hygienically safe; Pb, Cu, Ni, and Zn concentrations were much lower than regulatory limits for land use of sewage sludge. Cd, Hg, As, and Cr were not detected in granules. Application of granules at 30 t/ha and 60 t/ha significantly improved soil quality and increased crop yield by up to 176 ± 14 %. The supplement ratio was significantly negatively correlated with the soil bulk density and positively correlated with the soil porosity, organic matter, and humus in soil. Heavy metals in crops remained within safe limits, with minor variations observed. Soil porosity, ammonium nitrogen, and organic matter were the main environmental factors driving bacterial community differences and causing significant shifts towards beneficial bacterial families, enhancing soil health by suppressing harmful pathogens. This research underscores the potential of septic tank slurry granules to improve soil quality and support sustainable land use, offering valuable insights for urban waste management strategies.
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•Septic tank slurry was successfully converted into sanitary, nutrient-rich granules.•The field use of the granules notably improved soil fertility and physical properties.•Environmental and health risks from the sustainable land use of granules were discussed.•Heavy metals in granules had little effect on the soil and plants after land use of granules.•Bacterial communities shifted to beneficial bacteria, boosting soil health by reducing pathogens.
The spatial distribution and adsorption capacity of extracellular polymeric substances (EPS) were systematically investigated for waste activated sludge (WAS) treated by a short-time aerobic ...digestion (STAD) process. During the STAD process, both the slime and the loosely bound EPS (LB-EPS) increased first and then decreased, while the tightly bound EPS (TB-EPS) gradually increased all the way. The variations of the fluorescence intensities at peaks A and B for the slime, the LB-EPS and the TB-EPS were consistent with the above variation of their concentrations. In the initial stage of the STAD process, aeration scour was mainly responsible for the release of LB-EPS and TB-EPS, which further resulted in the increase of slime and LB-EPS. Meanwhile, newly secreted EPS by microorganisms led to the increase of TB-EPS. In the later stage of the STAD process, the biodegradation of soluble organic matter caused the concentration decrease of both slime and LB-EPS. The Pb
2+
adsorption capacity by LB-EPS, TB-EPS and total EPS gradually increased with the increasing of STAD time, suggesting that the LB-EPS and TB-EPS played a key role in the adsorption of Pb
2+
and the LB-EPS had a higher adsorption capacity. FTIR results further indicated that STAD could improve the amounts of functional groups, especially for -OH, -COOH and -NH
2
in both LB-EPS and TB-EPS responsible for the binding of heavy metals, resulting in the increased adsorption capacity of EPS. Disclosing the influencing characteristics of the STAD process on the spatial distribution and the adsorption capacity of EPS in WAS for the first time, this work lays a foundation for the application of the STAD process in the reuse of WAS.
The spatial distribution and adsorption capacity of extracellular polymeric substances (EPS) were systematically investigated for waste activated sludge (WAS) treated by a short-time aerobic digestion (STAD) process.
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