Key factors governing alkaline pretreatment of waste activated sludge

Alkaline pretreatment is an effective technology to disintegrate sewage sludge, where alkali dosage and sludge concentration are two important factors. p H value or alkali concentration is usually adjusted in order to determine a proper dosage of alkali. Our work has found that this is not a good strategy. A new parameter, the ratio of alkali to sludge(Ra/s), is more sensitive in controlling the alkali dosage. The sludge concentration Csand retention time t are two other important factors to consider. The validity of these arguments is confirmed with modeling and experiments. The individual effect of Ra/s, Csand t was studied separately. Then the combined effect of these three factors was evaluated. The sludge disintegration degree of 44.7% was achieved with the optimized factors. Furthermore, an alkaline-microwave combined pretreatment process was carried out under these optimized conditions. A high disintegration degree of 62.3% was achieved while the energy consumption of microwave was much lower than previously reported.

Optimisation Strategy of Carbon Dioxide Methanation Technology Based on Microbial Electrolysis Cells

Microbial Electrolytic Cell(MEC)is an electrochemical reaction device that uses electrical energy as an energy input and microorganisms as catalysts to produce fuels and chemicals.The regenerative electrochemical system is a MEC improvement system for methane gas produced by biological carbon sequestration technology using renewable energy sources to provide a voltage environment.In response to the influence of fluctuating disturbances of renewable electricity and the long system start-up time,this paper analyzes the characteristics of two strategies,regulating voltage parameter changes and activated sludge pretreatment,on the methane production efficiency of the renewable gas electrochemical system.In this system,the methane production rate of regenerative electrochemical system is increased by 1.4 times through intermittent boosting start-up strategy;based on intermittent boosting,the methane production rate of regenerative electrochemical system is increased by 2 times through sludge pyrolysis pretreatment start-up strategy,and the start-up time is reduced to 10 days.Meanwhile,according to the simulation test results of power input fluctuation and intermittency,the stability standard deviation of its system operation is 75%of the original one,and the recovery rate is about 1 times higher.This study can provide a theoretical basis and technical reference for the early industrial application of microbial CO_(2)methanation technology based on renewable energy.

Anaerobic digestion of sludge by different pretreatments:Changes of amino acids and microbial community

Many studies have investigated the effects of different pretreatments on the performance of anaerobic digestion of sludge.However,the detailed changes of dissolved organic nitrogen,particularly the release behavior of proteins and the byproducts of protein hydrolysis-amino acids,are rarely known during anaerobic digestion of sludge by different pretreatments.Here we quantified the changes of three types of proteins and 17 types of amino acids in sludge samples solubilized by ultrasonic,thermal,and acid/alkaline pretreatments and their transformation during anaerobic digestion of sludge.Tryptophan protein,aromatic protein I,aromatic protein II,and cysteine were identified as the key dissolved organic nitrogen responsible for methane production during anaerobic digestion of sludge,regardless of the different pretreatment methods.Different from the depletion of other amino acids,cysteine was resistant to degradation after an incubation period of 30 days in all sludge samples.Meanwhile,the“cysteine and methionine metabolism(K00270)”was absent in all sludge samples by identifying 6755 Kyoto Encyclopedia of Genes and Genomes assignments of genes hits.Cysteine contributed to the generation of methane and the degradation of acetic,propionic,and n-butyric acids through decreasing oxidation-reduction potential and enhancing biomass activity.This study provided an alternative strategy to enhance anaerobic digestion of sludge through in situ production of cysteine.

Optimization of H_2O_2 dosage in microwave-H_2O_2 process for sludge pretreatment with uniform design method

A microwave-H202 process for sludge pretreatment exhibited high efticiencies of releasing organics, nitrogen, and phosphorus, but large quantifies of H202 residues were detected. A uniform design method was thus employed in this study to further optimize H202 dosage by investigating effects of pH and H202 dosage on the amount of 1-I202 residue and releases of organics, nitrogen, and phosphorus. A regression model was established with pH and H202 dosage as the independent variables, and H202 residue and releases of organics, nitrogen, and phosphorus as the dependent variables. In the optimized microwave-H202 process, the pH value of the sludge was firstly adjusted to 11.0, then the sludge was heated to 80~C and H202 was dosed at a H202 ：mixed liquor suspended solids （MLSS） ratio of 0.2, and the sludge was finally heated to 100~C by microwave irradiation. Compared to the microwave-H202 process without optimization, the H202 dosage and the utilization rate of H202 in the optimized microwave-H202 process were reduced by 80% and greatly improved by 3.87 times, respectively, when the H202：MLSS dosage ratio was decreased from 1.0 to 0.2, resulting in nearly the same release rate of soluble chemical oxygen demand in the microwave-H202 process without optimization at H202：MLSS ratio of 0.5.

Effect of organic matter on phosphorus recovery from sewage sludge subjected to microwave hybrid pretreatment

Microwave（MW） hybrid processes are able to disrupt the flocculent structure of complex waste activated sludge,and help promote the recovery of phosphorus as struvite.In this study,to optimize struvite yield,（1） the characteristics of matter released in MW-hybrid treatments were compared,including MW,MW-acid,MW-alkali,MW-H2O2,and MW-H2O2- alkali.The results showed that selective release of carbon,nitrogen,phosphorus,Ca^2＋,and Mg^2＋ achieved by sludge pretreatment using MW-hybrid processes.MW-H2O2 is the recommended sludge pretreatment process for phosphorus recovery in the form of struvite.The ratio of Mg^2＋：NH4^＋-N：PO4^3--P was 1.2：2.9：1 in the supernatant.（2） To clarify the effects of organic matter on struvite recovery,the composition and molecular weight distribution of organic matters were analyzed.Low molecular weight COD was found to facilitate the removal rate of NH4^＋-N and PO4^3-P via crystallization,and the amorphous struvite crystals（〈1 kDa） from the filtered solutions had high purity.Therefore,the present study reveals the necessity of taking into consideration the interference effect of high molecular weight organic matters during struvite crystallization from sewage sludge.

An executive review of sludge pretreatment by sonication

Ultrasonication（US）, which creates hydro-mechanical shear forces in cavitation, is an advanced technology in sludge pretreatment. However, there are many factors affecting the efficacy of cavitation and ultrasonication disintegration of sludge as a consequence.The objective of this work is to present an extensive review of evaluation approaches of sludge US pretreatment efficiency. Besides, optimization methodologies of related parameters,the differences of optimum values and the similarities of affecting trends on cavitation and sludge pretreatment efficiency were specifically pointed out, including ambient conditions,ultrasonic properties, and sludge characteristics. The research is a prerequisite for optimization of sludge US pretreatment efficiency in lab-scale and practical application. There is not-yet a comprehensive method to evaluate the efficiency of sludge US pretreatment, but some main parameters commonly used for this purpose are degree of sludge disintegration, proteins,particle size reduction, etc. Regarding US parameters, power input PUS, intensity IUS, and frequency FSseem to have significant effects. However, the magnitude of the effect of PUSand probe size in terms of IUShas not been clearly detailed. Investigating very low FSseems interesting but has not yet been taken into consideration. In addition, static pressure effect has been marginally studied only and investigation on the effect of pH prior to US process has been restricted. Their effects therefore should be varied separately and simultaneously with other related parameters, i.e. process conditions, ultrasonic properties, and sludge characteristics, to optimize sludge US pretreatment process.