[Effects of Heat and Heat-alkaline Treatments on Disintegration and Dissolved Organic Matter in Sludge].

The hydrolysis of sludge organic matter is the rate-limiting step of anaerobic sludge digestion. Because pretreatments can effectively convert the solid organic matter into dissolved organic matter, it can improve the degradation rate and methane conversion rate of organic matter. In this study, the effects of heat and heat-alkaline treatments (two common pretreatments) on the composition, relative molecular weight distribution, and structure of dissolved organic matter in sludge were studied. The results showed that the heat and heat-alkaline treatments released a large amount of organic matter, which resulted in the SCOD increasing 21.9 times (heat treatment) and 47.8 times (heat-alkaline treatment). These pretreatments changed the molecular weight distribution of dissolved organic matter and decreased the molecular weight of the organic matter to the greatest degree. The results of three-dimensional fluorescence spectroscopy showed that both of the pretreatments can hydrolyze protein, the main component of sludge soluble organic matter, with the heat-alkaline treatment being more significant. In dissolved organic matter, the byproducts of the microorganisms and humic acids are not easily hydrolyzed further by the two pretreatments. In addition, the two pretreatments led to the appearance of new organic structures and the change and even disappearance of the original organic matter.

[Impacts of alkaline thermal treatment on characteristics of sludge from sewage treatment plant].

Alkaline thermal treatment is an important pretreatment method for sewage sludge. In this paper, in order to optimize the alkaline thermal treatment conditions for sludge pretreatment, four pretreatment parameters ( sludge concentration, pH, temperature and treatment time) were investigated through orthogonal experiments to determine their effects on the sludge disintegration, sludge concentration and sludge morphology of sewage sludge. The experimental results showed that the significance of the four factors on sludge characteristics was in the order of pH > temperature > treatment time > sludge concentration. Additionally, the optimal conditions of the four factors for the release of soluble chemical oxygen demand (SCOD) of unit sludge and decrease of sludge concentration were as follows: 36.55 g x L(-1), pH 12.45, 175 degrees C and 60 min. While the optimal conditions for the decrease of particle size and fractal dimension were 36.55 g x L(-1), pH 12.5, 175 degrees C and 45 min.

[Releases of carbon, nitrogen and phosphorus from sewage sludge at different microwave energy inputs].

In this study, the releases of carbon, nitrogen and phosphorus from sludge treated by microwave irradiation were investigated by batch experiments at two microwave energy inputs (MEIs), 54 kJ and 108 kJ. The final temperatures of the treated samples at these two MEIs were about 56 degrees C and 90 degrees C, respectively. Results showed that the higher MEI was more helpful to release TC, TOC, TN and TP from sludge treated by microwave. The release rates of TC, TN and TP were doubled at the MEI of 108 kJ than that of 54 kJ, and their highest rates were 5.26%, 22.06% and 33.15%, respectively. The MLSS significantly affected releases of TOC, TC, TN, NH4+ -N, TP and ortho-PO4(3-). However, the microwave power (MWP) had no significant effect on these releases except IC. The normalization of these parameters, representing the energy efficiencies of treating sludge, clearly showed that the P (TP) was the highest and the P(IC) was the lowest. However, the average values of P(IC), P(NH4+ -N) and P(ortho-PO4(3-)) decreased at the same MISS concentration, respectively, about 67%, 73% and 56% when the MEI doubled from 54 kJ to 108 kJ.

[Impacts of different pretreatments on characteristics of excess sludge].

The impacts of three pretreatments (acid, alkaline and thermal treatments) on the characteristics of sludge were discussed. The results showed that the three pretreatments could disintegrate the sludge and the effectiveness of alkaline treatment was the maximum (about 58.46%) and its SCOD release was also the maximum (2934.9 mg/L). The main compositions of soluble organics were proteins, carbohydrates and volatile fatty acids (about 80%-90%, together). The increase of soluble proteins in the alkaline treated sludge was the maximum (2058.6 mg/L), while the increase of soluble carbohydrates in the thermal treated sludge was the maximal (353.2 mg/L). The SS and VSS of sludge were decreased by the treatments and the effectiveness of alkaline treatment was the best and that of acid treatment was the worst. The particle size distribution of sludge showed acid and alkaline treatments could decrease the particle size and increase the consistency of sludge. The solublized mechanism of the three pretreatments was also discussed.

[Non-filamentous sludge bulking caused by low concentration of dissolved oxygen and phosphorus deficiency and its control].

Non-filamentous sludge bulking occurred during sludge acclimation in lab-scale bio-reactors and the characteristics, properties and degrading pollutants capability of non-filamentous sludge were analyzed. Both low DO concentration (0 - 0.7 mg/L) and low ratio of P/BOD5 (0.78/100) resulted in excessive proliferation of viscous zoogloea and sludge bulking. SVI was directly proportional to extracellular polysaccharides and was inversely proportional to hydrophobicity of sludge. The sludge bulking could be effectively controlled by increasing DO concentration and P/BOD5 ratio. Besides, adding some porous padding into viscous bulking sludge was a useful method which might avoid the deterioration of sludge settlement and maintain good performance in the system. The viscous bulking sludge could not be controlled by addition of NaC1O.

[Study on treatment of excess sludge under alkaline condition].

Disintegration of alkaline treatment on excess sludge and its influencing factors were investigated. The results show that alkaline treatment can increase the soluble chemical demand oxygen (SCOD) by releasing the organic materials from cells to water and converting the insoluble ones to soluble ones. The floc structures and the cell structures of sludge were destroyed in the process of alkaline treatment when the treated pH value was above 11.0. OH- played the role in the alkaline treatment and the cation would impact the efficiency. The maximal removal of volatile solid (VS) were 48.01% and 40.40% for total solid (TS) when the pH value was 13.0. Sludge size reduced with the increase of pH value. Sludge concentration, pH value and treatment time were three important factors of alkaline treatment. The results of orthogonal experiment indicated that the sludge concentration was a marked factor of affecting the efficiency of alkaline treatment, but the SCOD of unit sludge was almost similar.

Effects of thermally pretreated temperature on bio-hydrogen production from sewage sludge.

Hydrogen can be obtained by anaerobic fermentation of sewage sludge. Therefore, in this paper the effects of thermally pretreated temperatures on hydrogen production from sewage sludge were investigated under different pre-treatment conditions. In the thermal pretreatment, some microbial matters of sludge were converted into soluble matters from insoluble ones. As a result, the suspended solid (SS) and volatile suspended solid (VSS) of sludge decreased and the concentration of soluble COD (SCOD) increased, including soluble carbohydrates and proteins. The experimental results showed that all of those pretreated sludge could produce hydrogen by anaerobic fermentation and the hydrogen yields under the temperatures of 121 degrees C and 50 degrees C were 12.23 ml/g VS (most) and 1.17 ml/g VS (least), respectively. It illuminated that the hydrogen yield of sludge was affected by the thermally pretreated temperatures. Additionally, the endurance of high hydrogen yield depended on the translation of microbial matters and inhibition of methanogens in the sludge. The temperatures of 100 degrees C and 121 degrees C (treated time, 30 min) could kill or inhibit completely the methanogens while the others could not. To produce hydrogen and save energy, 100 degrees C was chosen as the optimal temperature for thermal pretrcatment. The composition changes in liquid phase in the fermentation process were also discussed. The SCOD of sludge increased, which was affected by the pretreatment temperature. The production of volatile fatty acids in the anaerobic fermentation increased with the pretreatment temperature.