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The cultivation of Chlorella vulgaris in sludge extract (SE) from municipal excess sludge diluted with BG11 medium was investigated to achieve sludge reduction and microalgae cultivation. A maximum biomass of 1.404 ± 0.101 g/L was achieved at 15 days in a mixture of 25% BG11 and 75% sludge extract under 10,000-lx light. In early culture periods, heterotrophy dominated the process in the group with a high proportion of sludge extract of excess sludge extract containing relatively high amounts of organic material, which led to enhanced citrate synthase enzyme activities and reduced rubisco enzyme activities. Moreover, increasing the light intensity did not significantly improve biomass production due to its inhibitory effects on respiration in the early culture stages. The response surface model showed that organic matter was the main factor influencing biomass production from 0 to 2 days. The influence of light intensity on biomass production became more noticeable only after depleting the organic matter in sludge extract.

As a common pretreatment process for coal chemical wastewater, the conventional one-stage coagulation process has the problem of poor removal of small size oil, which will inhibit the subsequent biological treatment. Measures to improve oil removal efficiency based on the development of new coagulants and the addition of composite processes are common in the literature, but two-stage coagulation to improve coagulation efficiency has not been reported to date. Here, we optimized coagulation parameters and compared the oil removal efficiency of two-stage coagulation and one-stage coagulation. Under the same total dosage of coagulant (PAC), the optimum removal of oil in two-stage coagulation was achieved 90% which increased by 11% compared to one-stage process. P10 and P 1 μm were proposed to evaluate the oil removing effect of two-stage coagulation. In addition, SEM scanning was used to conduct flocs analysis and two-stage coagulation process simulation, revealing the principle of the excellent oil removal performance of two-stage coagulation. Finally, coagulant in filter residue was recovered by acidification method and the recovered coagulant was used again in the two-stage coagulation process of coal chemical wastewater. These results suggest that two-stage coagulation is a cost-effective alternative oil removal technique with high energy efficiency and environmental benign. This research may offer helpful insights to develop an advanced oil removal process.

The correlation between sludge reduction induced by 2,4,6-trichlorophenol (2,4,6-TCP) as an uncoupler and sludge toxicity was investigated in sequence batch reactors over a 100-d operation period. The influent concentrations of 2,4,6-TCP tested were 10 mg/L, 30 mg/L, and 50 mg/L. Sludge reduction, chemical oxygen demand (COD) removal rate, and sludge toxicity were measured. The results showed that from 30 to 80 d, when the COD removal rate was at an acceptable level, the sludge reduction levels for the 10 mg/L, 30 mg/L, and 50 mg/L groups were 9.7%, 31.6%, and 41.5%, respectively, and the average sludge toxicity values were 24.2%, 38.0%, and 53.0%, respectively. Sludge reduction was positively correlated with sludge toxicity. The two-dimensional polyacrylamide gel electrophoresis/results showed that extracellular and intracellular proteins secreted by the activated sludge during uncoupling metabolism were positively correlated with sludge toxicity. Taking the COD removal rate, sludge reduction, and sludge toxicity into consideration, the optimal influent concentration of the uncoupler 2,4,6-TCP was 30 mg/L when the initial mixed liquid suspended solids of sludge was 2,500 mg/L.

High concentration of nitrogen and phosphorus and imbalance of N/P can lead to the formation of water and the malignant proliferation of toxic microalgae. This study put forward the advanced nutrient removal with the regulation of effluent N/P as the core in order to restrain the eutrophication and growth of poisonous algae. According to the preliminary study and review, the optimal N/P for non-toxic green algae was 50:1. The horizontal sub-surface flow constructed wetland was filled with steel slag and ceramsite to achieve the regulation of effluent N/P. The results showed that steel slag had the stable P removal capacity when treating synthetic solution with low P concentration and the average removal rate for 1.5, 1.0, and 0.5 mg/L synthetic P solution was 2.98 ± 0.20 mg kg−1/h, 2.26 ± 0.15 mg kg−1/h, and 1.11 ± 0.10 mg kg−1/h, respectively. Combined with P removal rate and P removal task, the filling amount of steel slag along the SSFCW (sub-surface flow constructed wetland) was 3.22 kg, 4.24 kg, and 4.31 kg. In order to ensure the stability of dephosphorization of steel slag, the regeneration of P removal capacity was investigated by switching operation of two parallel SSFCW in 20 days for cycle. The N removal was limited for the deficiency of carbon source (COD (chemical oxygen demand)/TN = 3–4), and was stable at 18.5–31.9% which was less affected by temperature. Therefore, by controlling the process of quantitative P removal of steel slag, the effluent N/P in SSFCW can be stable at 40–60:1 in the whole year, so as to inhibit the malignant proliferation of toxic algae.

The aerobic biodegradation rate, organic toxicity and microbial community structure of activated sludge acclimated by catechol, resorcinol and hydroquinone were investigated, to study the relationship between microbial structure and sludge organic toxicity caused by phenolic compounds. At the stable operation stage, the degradation rates of the dihydroxy benzenes in a single sequencing batch reactor (SBR) cycle were followed the order: resorcinol (89.71%) > hydroquinone (85.64%) > catechol (59.62%). Sludge toxicity bioassay indicated that the toxicity of sludge was catechol (45.63%) > hydroquinone (40.28%) > resorcinol (38.15%). The accumulation of secondary metabolites such as 5–10 kDa tryptophan and tyrosine protein substances caused the differential sludge toxicity. Microbial metagenomic analysis showed that the toxicity of sludge was significantly related to the microbial community structure. Thauera, Azoarcus, Pseudomonas and other Proteobacteria formed in the sludge during acclimation. Catechol group had the least dominant bacteria and loop ring opening enzyme genes (catA, dmpB, dxnF, hapD) numbers. Therefore, the degradation of catechol was the most difficult than resorcinol and hydroquinone, resulting the highest sludge toxicity.

BACKGROUND: The cultivation of Chlorella vulgaris present in toxic sludge extract from resorcinol‐rich wastewater was investigated to simultaneously determine the biomass production and toxicity removal. RESULTS: A comparison of the blank and the toxic sludge extract revealed that the sludge toxicity originating from the degradation of resorcinol was highly correlated to the mass fraction at 5000–10000 Da (R = 0.987, P = 0.013) and led to a decline in biomass (1.49 g L⁻¹ to 1.36 g L⁻¹ in 30 days) along with a reduced utilization rate of organics in the sludge extract, especially in the early stage (0–5 days) of culture. The effects of sludge toxicity were characterized by the downregulation of proteins associated with carbon (C) metabolism and the upregulation of proteins involved in photoreaction by proteomics. CONCLUSION: The sludge toxicity directly caused a decline in biomass production of C. vulgaris resulting from the downregulation of C metabolism. However, the promotion of biomass for heterotrophism was more significant than the inhibitory effect in the toxic sludge extract when compared with BG11 medium. © 2018 Society of Chemical Industry

Chlorella vulgaris was cultivated in different proportions of activated sludge extracts, which was from the treatment of synthetic wastewater containing tetrachlorophenol. The growth period of C. vulgaris could be shortened for about 10 days when sludge extract was mixed into BG11 culture substrate, and the growth of C. vulgaris was promoted during the period of adaptation and logarithmic period. In the stable and decay period, when the proportion of sludge extract increased to 50%, cell proliferation was inhibited. There was an evident positive correlation between the total and average amount of starch polysaccharide with sludge concentration. When C. vulgaris was cultivated with pure sludge extracts, the total amount of starch and polysaccharide was up to 103 and 125 mg/L. Therefore, the low-toxic sludge extracts were more beneficial to the accumulation of carbohydrates. In the 100% sludge extracts culture medium, chlorophyll-a in C. vulgaris was accumulated to 30.2 mg/L on the 25th day. Through the analysis of algal cells' ultrastructures, it was shown that the photosynthesis was strengthened greatly with low-toxic sludge extracts. The results show that the rich heterotrophic carbon source in the sludge extract can be used as an excellent medium for Chlorella. It provides new ideas for the harmless utilization of surplus sludge as a resource. At the same time, the use of nutrients in the sludge extract to cultivate Chlorella is of great significance to low-cost algae cultivation.

Coal gasification wastewater is mainly from gas washing, condensation and purification processes in the gas furnace with high NH3-N (nitrogen in water in the form of free ammonia (NH3) and ammonium ion (NH4+)), TN (total nitrogen) and refractory organics content, which will inhibit the subsequent biological treatment. The ‘air stripping – hydrolysis acidification – air stripping’ process was proposed as the pretreatment for coal gasification wastewater to improve the biodegradability and nitrogen removal, which could reduce the subsequent biological treatment load. The first-stage air stripping process before hydrolysis acidification could achieve a significant removal of NH3-N (97.0%) and volatile phenol (70.0%), reducing the corresponding toxicity on hydrolysis acidification. The group with air stripping had more abundant microbial communities and a more effective organic degradation performance in hydrolysis acidification than that without air stripping. The second-stage air stripping removed NH3-N released from hydrolysis acidification, and significantly reduced the TN concentration in effluent. The whole process achieved a TN removal from 2,000 ± 100 mg/L to 160 ± 80 mg/L, and a total phenols removal from 700 ± 50 mg/L to 80 ±20 mg/L.

The increasing production of toxic sludge becomes the limiting factor of sludge resource utilization. In this study, the source of sludge toxicity and the best way for toxic organic reduction was investigated. Four disintegration methods (freeze/thaw, ultrasonication, alkali-thermal hydrolysis and ozonation) were used to analyze the release of organic matter and sludge toxicity reduction. Ultrasonication (SCOD = 5120.4 ± 67.8 mg L−1) was the best way to break sludge and remove toxicity among four methods, which dissolution rate was more than 80%, and the total toxicity inhibition rate could be reduced to 64.3 ± 4.2%, significantly reducing the toxicity of sludge. Gel chromatography (GPC) showed that the disintegration could convert refractory macromolecular organics (MW > 10 kDa) into small molecular substances (MW