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Excessive nitrogen emission is a common problem in the secondary effluents of rural wastewater treatment facilities. Nitrogen could be removed by constructed wetlands and ecological floating beds, but these techniques have low purification capacity in practice. Here, a novel tubular reactor-enhanced ecological floating bed was developed to enhance nitrogen removal of secondary effluents. We tested the feasibility of this system during a long-term operation. Results show that our system achieves a removal efficiency of secondary effluent N of 82.2% for 30 days after start-up and then maintains this efficiency for an additional 220 days. Dissolved oxygen was reduced from 2.92 to 0.23 mg L−1, and the CODCr/TN (C/N) ratio increased from 2.6 to 13.1 along the reactor channel. This finding is explained by the synergy between the unique tubular reactor configuration and the mixed filler: palm fiber and bagasse. This environment enhances the spatial distribution of nitrifiers and denitrifiers along the channel, which was further demonstrated by scanning electron microscopy and high-throughput sequencing.

A landfill bio-cover material for methane bio-oxidation was explored using aged refuse coupled with leachate. It was found that the aged refuse taken from an 8-year landfill could be used for the bio-oxidation of methane generated from landfill; moreover, the bio-oxidation ability was further enhanced in the presence of leachate. The highest methane oxidation capacity of 390 g \({{\rm CH}_{4}/({\rm m}^{2}}\) day) was obtained for the aged refuse modified with the leachate from aged-refuse bio-filter, close to the performance of compost. Leachate with extremely high organic matter content, however, was unfavorable for the growth of methane bio-oxidation Methanotrophs in aged refuse presumably because of oxygen consumption during organic matter degradation process. Thus, the recommended properties of leachate should be as follows: \({{\rm NH}_{4}^{+}}\)-N 500 mg/L. In addition, the organic matter and water contents in aged refuse after modified by leachate need to be controlled at 15.0–18.0 and 31.4–32.1 %, respectively, for the purpose of efficient Methanotrophs metabolisms. Practical use of this novel bio-cover in real landfills cannot only control greenhouse gas emission, but promote the recycle and reuse of aged refuse, and simultaneous high-strength leachate treatment.

Total concentrations of heavy metals (Cu, Zn, Pb, Cr, Cd, and Ni) were measured among 63 samples of construction and demolition (C&D) wastes collected from chemical, metallurgical and light industries, and residential and recycled aggregates within China for risk assessment. The heavy metal contamination was primarily concentrated in the chemical and metallurgical industries, especially in the electroplating factory and zinc smelting plant. High concentrations of Cd were found in light industry samples, while the residential and recycled aggregate samples were severely polluted by Zn. Six most polluted samples were selected for deep research. Mineralogical analysis by X-ray fluorescence (XRF) spectrometry and X-ray diffraction (XRD), combined with element speciation through European Community Bureau of Reference (BCR) sequential extraction, revealed that a relatively slight corrosion happened in the four samples from electroplating plants but high transfer ability for large quantities of Zn and Cu. Lead arsenate existed in the acid extractable fraction in CI7-8 and potassium chromium oxide existed in the mobility fraction. High concentration of Cr could be in amorphous forms existing in CI9. The high content of sodium in the two samples from zinc smelter plants suggested severe deposition and erosion on the workshop floor. Large quantities of Cu existed as copper halide and most of the Zn appeared to be zinc, zinc oxide, barium zinc oxide, and zincite. From the results of the risk assessment code (RAC), the samples from the electroplating factory posed a very high risk of Zn, Cu, and Cr, a high risk of Ni, a middle risk of Pb, and a low risk of Cd. The samples from the zinc smelting plant presented a high risk of Zn, a middle risk of Cu, and a low risk of Pb, Cr, Cd, and Ni.

In this work, the enhanced dewaterabing characteristics of waste activated sludge using Fenton pretreatment was investigated in terms of effectiveness and statistical optimization. Response surface method (RSM) and central composite design (CCD) were applied to evaluate and optimize the effectiveness of important operational parameters, i.e., H2O2 concentrations, Fe2+ concentrations and initial pH values. A significant quadratic polynomial model was obtained (R2= 0.9189) with capillary suction time (CST) reduction efficiency as the response. Numerical optimization based on desirability function was carried out. The optimum values for H2O2, Fe2+, and initial pH were found to be 178 mg·g−1 VSS (volatile suspended solids), 211 mg·g−1 VSS and 3.8, respectively, at which CST reduction efficiency of 98.25% could be achieved. This complied well with those predicted by the established polynomial model. The results indicate that Fenton pretreatment is an effective technique for advanced waste activated sludge dewatering. The enhancement of sludge dewaterability by Fenton’s reagent lies in the migration of sludge bound water due to the disintegration of sludge flocs and microbial cells lysis.