Applied Mechanics and Materials Vol. 768

Abstract: The nitrogen conversion with attention to the intermediates and NOx precursors has been investigated during the primary pyrolysis of sewage sludge by using Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analyzer (TGA) coupled with Fourier transform infrared spectrometry (FTIR). The results indicated that 75.4% of total nitrogen exists in the forms of protein in the sewage sludge. Amine compounds and nitrogen heterocyclics were found to be the main nitrogenated intermediates during the pyrolysis process in the temperature range of 250-400 °C. As the dominant nitrogenated compounds, the relative proportions of amine compounds were above 52% in all cases. And since the decomposition of sewage sludge was promoted by high temperature, the relative proportion of amine compounds increased by 24.6% when the temperature raised from 300 to 400 °C. Moreover, the generation of NH₃ at 250 ^oC was mainly derived from the decomposition of ammonium salt, while the deamination of amine compounds led to a significant increase of NH₃ at 300 °C.

Abstract: This study aims to find out the optimum extraction time varied from 5 min to 60 min for extracellular polymeric substances (EPS) from sewage sludge pretreated at 80 °C. The change of the contents of EPS and its components under different time limit were recorded and compared. The results showed: the contents of soluble protein, TOC, soluble sugar and DNA was increased by 579.17 mg/l, 514.25 mg/l, 132.79 mg/l, and 34.69 mg/l, respectively, with the increase of thermal pre-treatment time during the process, and the DNA content increased the least, which indicating that the effect of thermal pre-treatment at 80 °C on cell lysis of sewage sludge was small. The EPS content, as a whole, was increased with the increase of thermal pre-treatment time. By analyzing the experimental data with the Analytic Hierarchy Process Model, which was used to identify the optimum thermal pre-treatment time of extracting EPS, the results showed that the effectiveness of EPS extraction from sludges was 30 min>60 min>50 min>20 min>40 min>10 min>5 min. Therefore, the 30 min was choosed as the optimum thermal pre-treatment time.

Abstract: We focused on the effects of ultrasound and Fenton reagent in ultrasonic coupling Fenton oxidation (U+F) pre-treatment processes on the disintegration of wastewater treatment plant sludge. The results demonstrated that U+F treatment could significantly increase SCOD, TOC, total N, proteins, total P and PO₄^3- concentrations in sludge supernatant. This method was more effective than ultrasonic (U) or Fenton oxidation (F) treatment alone. U+F treatment increased the SCOD by 2.1-and 1.4-fold compared with U and F alone, respectively. U+F treatment increased the total N and P by 1.7-and 2.2-fold, respectively, compared with F alone. This demonstrated that U+F treatment induces disintegration of sludge and release of organic carbon, nitrogen and phosphorus better.

Abstract: Sludge moisture content was investigated at different stages during the test. Pilot-scale sludge drying bed and sludge drying reed beds had the same size of 3 m×1 m×1.3 m, and the bed height consisted of a 65 cm media layer and a 65 cm extra height. The media layer is filled with slag (20 cm), gravel (20 cm), coarse sand (5 cm) and quartz sand (24.5 cm) from the bottom in turn. Unit 1 was a conventional sludge drying bed, unit 2 was a sludge drying reed bed. Unit 1 and unit 2 had ventilation pipes which were mounted on the drainage pipes. Unit 3 was a sludge drying reed bed without ventilation pipe. The waste activated sludge was feed into the three units periodically during the experiment. The experiment investigated the sludge moisture content. At the end of the operation, the sludge moisture content in three units decreased by 18.52%, 22.37%, and 20.68%, respectively. It was found that the dewatering effect of the sludge drying reed bed was better than the conventional drying bed. The effect of plant growth on sludge dewatering is greater than the ventilation, but the difference was not significant.

Abstract: To develop new clean energy has become an urgent task for many countries forced by the energy and environment crisis. To make biodiesel from sewage sludge is one of the solutions. In this study, biodiesel production from sewage sludge by in situ transesterification was discussed. The solvent is methanol and catalyst is sulfuric acid. In-situ transesterification, has many merits over conventional transesterification reaction such as it simply the procedure by skipping the step of lipid extraction and as a result cost can be saved. That is, the steps — sludge dissolved, lipid extraction and transesterification reactions — take place simultaneously. Methanol acts as an extraction solvent and as an esterification reagent as well. Experiments were conducted to determine the optimal parameters of in-situ transesterification for maximizing the yield of biodiesel, which are methanol to sludge mass ratio, acid concentration and temperature. The optimum synthesis condition was determined by orthogonal test L₁₆ (4³), and it was found that an optimum biodiesel yield can be obtained from sewage sludge by in-situ transesterification (16.6%) at methanol to sludge mass ratio 10:1(w/w), H₂SO₄ concentration 5% (v/v), and temperature 65°C. Temperature, H₂SO₄ concentration, and methanol to sludge mass ratio in sequence had significant influence on FAMEs yield. The FAMEs in the product were analyzed by GC-MS and the purity can be higher than 96%.

Abstract: With Chinese continuous improvement of the urbanization and industrialization level, water pollution has becoming more and more serious, and the by-product —sludge has caught the focus of public attention. The total amount of sewage sludge produced in Beijing in 2010 is about 3,700t/d (wet base), 2,500t/d of which is from the urban area and 1,200t/d is from country side. Such a large amount of sludge with abundant water brought great difficulties to the subsequent processing. However, the cost of sludge treatment amounts to almost half of the sewage plant running cost while the consumption of drug covered more than half of the sludge treatment expenditure. Another aspect is that the water content of the dewatered sewage sludge is not stable, because of the variation of inlet amount and quality. Without knowing the relationship between the characteristics of sewage sludge and conditioning reagent, the operator just try to add more reagent, which in the end increase the cost of sludge treatment. Meanwhile, cationic polyacrylamide (C-PAM) is currently the most widely used sludge conditioning reagent. This research is to find out the relationship between the characteristics of sewage sludge and adding dosage of CPAM, which can be the first step to discuss how to adjust the conditioning reagent according to sewage sludge with different characteristics.Polyacrylamide (PAM) of different cationic (15%,35%,45%,60%), molecular weight (8 million, 10million, 12million) and dosage (2‰,3‰,4‰,5‰,6‰) are under testing in the experiment considering the index of capillary suction time (CST).Experimental material is the sludge from digestion tank in one of Beijing sewage plants. According to the experiment, it was found that the 8million-10million molecular weight, 4‰-6‰ adding dosage perform the best.

Abstract: Thermogravimetric analysis (TGA), coupled with Fourier transform infrared analysis (TG-FTIR) of sewage sludge was carried out to investigate the influence of moisture and oxygen on gas evolution during pyrolysis of sewage sludge. Wet sewage sludge with moisture of 86.47(wt. %) was collected from Shanghai, China. Wet sewage sludge and air dried sewage sludge were used in TG-FTIR analysis, while combustion (air flow) and pyrolysis (nitrogen flow) were separately introduced to achieve comparison. In condition of dry sewage sludge pyrolysis, there were two peaks representing release of separately moisture and volatile. Weight lost 85% in the temperature range of 25-600 °C while the main volatile matters were released before 600 °C. When air flow was introduced, a third peak of char combustion occurred. Wet sewage sludge made no much difference, except for the relatively outstanding peak of moisture release. Temperature regions for each stage were the same for wet and dry sewage sludge from TG curve. However, from the FTIR analysis, ammonia has two peaks between 50 and 450 °C in pyrolysis while ammonia has only one peak between 50 and 300°C.

Abstract: Municipal sewage sludge has been increasingly produced in China with the development of municipal wastewater treatment. The use of sewage sludge as a fertilizer and soil amendment has resulted in high concentrations of heavy metals in the soil and food limiting its use. Controlling the pollution of heavy metals is the key factor to realize the safe utilization of sewage sludge. The present study was carried out to find scientific basis to the appropriate sludge applications in agriculture and forestry. Pilot experiments in Eucalyptus forest showed that the total yield and nutrient amount of P. hydridum were significantly higher than A. marorrhiza, the annual average yield in dry weight and total nutrient amount of P. hydridum were 21.32 thm^-2 and 1248.2 kghm^-2, respectively, 9.18 times and 3.58 times that of A. marorrhiza, so P. hydridum were more suitable to be the converting plant from sludge to biochar or organic fertilizer. After plants treatment, the maturity of sludge increased significantly, water content and soluble heavy metals decreased obviously, so that the agricultural safety increased, and the all indicators were conformed to the sludge requirements for agricultural use. In addition, the Eucalyptus trees grow well with a large spread of sewage sludge. Nutrient contents of Eucalyptus forestland soil increased and heavy metal contents of the topsoil beneath the sludge did not significantly increase.

Abstract: The process of wastewater treatment is one of the sources of greenhouse gas emissions from urban human activities and methane is a source of greenhouse gases can not be ignored. According to the method recommended by IPCC Guidelines for National Greenhouse Gas Inventories 2006,a calculation model was established to assess methane emissions of wastewater treatment in Henan.Then methane emissions from wastewater treatment in Henan province in the year of 2010 were estimated. The results showed that net methane emissions from the sewage treatment process was 21,764.1 tons, and methane from the industrial wastewater generated process was 98,609.33 tons. The results will provide a scientific basis for policy maker to mitigate the methane emission from the sewage treatment process of Henan province.

Abstract: In this work, modified fly ash by Na₂CO₃ was prepared and used to remove the Cr (VI) in simulate wastewater, which was rarely reported in domestic and foreign. In the meantime, every single-factor experiment, which maybe influenced the removal ratio of Cr (VI), was done. The major-minor order of test factors and the optimum combination processing conditions influencing the treatment effects of Cr (VI) were determined according to the orthogonal experiment. The results showed that the major-minor order was initial concentration of Cr (VI), dosage of modified fly ash, adsorption duration, temperature and pH values. And the optimum combination of above discussed factors was 15 mg/L, 5 g, 90 min, 30 oC and 2.5, respectively. Under this optimum condition, the removal rate of Cr (VI) can reach more than 74.86%, approximately 1.35 times compared to that of original fly ash.