Comparative Study On Improvement Of Sludge Dewaterability By Chemical And Biological Conditioning Based On CaO₂ And Filamentous Fungi

A large amount of excess sludge is produced during the biological treatment process of wastewater.Excess sludge needs to be dewatered before final disposal for two reseaons:firstly,sludge volume is greatly reduced after dewatering,facilitating storage and transportation;secondly,facilitating the subsequent disposal process,such as incineration,landfill and land utilization.In order to improve sludge dewaterability and dewatering efficiency,conditioning agent is usually added to sludge before sludge dewatering.However,currently used chemical conditioners are prone to secondary pollution,and have certain ecological risks.Therefore,the development of environment-friendly new sludge conditioners has become an urgent need for sludge dewatering industry.In this study,two environment-friendly sludge conditioning methods,i.e.calcium peroxide?CaO₂?conditioning and filamentous fungi conditioning,were studied.The main research contents and results are as follows:?1?Enhancement of sludge dewaterability by CaO₂ conditioning and its mechanismAddition of CaO₂ to sludge could effectively reduce sludge specific resistance?SRF?.Single factor experiments showed that when the CaO₂ dosage was 20 mg/g DS,sludge SRF was reduced by 37.9%compared with the unconditioned sludge,sludge dewaterability was improved by CaO₂ conditioning.The mechanism of CaO₂ conditioning to improve sludge dewaterability was mainly included in two aspects:On the one hand,CaO₂ could oxidize sludge and therefore effectively release the bound water in sludge.On the other hand,calcium ions produced by dissolution of CaO₂ could promote flocculation of sludge,and could also increase the zeta potential of sludge and reduce the repulsive force between the sludges.Single factor experiments and response surface methodology experiments showed that conditioning temperature,conditioning time and CaO₂ doase significant influence sludge SRF.The experimental results of plate and frame filter press showed that the dewatering rate of CaO₂-conditioned sludge and the moisture content of dewatered cake were 1.67 L/min and75.4%,respectively.The moisture content of dewaterd cake decreased by 4.9%compared with unconditioned sludge.?2?Optimization of filamentous fungi fermentation and pilot-scale productionCompared to fermentation with shake flask,the use of ventilated fermentor could greatly shorten the fermentation period of filamentous fungi Talaromyces flavus S1,and produced biomass was up to the highest on the second day,which was 12.80 g/L.During the fermentation process of filamentous fungi,polysaccharides were mainly used as organic substrates,a large number of N and P elements were consumed,and a large amount of soluble proteins were released by filamentous fungi.The optimum stirring speed for the formation of mycelial pellet was 120 rpm.Under this stirring speed,the average diameter of the mycelial pellet was 4.4 mm.When the stirring speed was too high or too low,filamentous fungi could not form mycelial pellet.Using biomass as the evaluation index,the optimum fermentation conditions for Talaromyces flavus S1 were as follows:an external carbon source concentration of 20 g/L,an external nitrogen source concentration of 0,and a ventilation rate of 1.2 vvm.The order of the influence of each factor on biomass was:ventilation rate>carbon source concentration>nitrogen source concentration.The pilot-scale production of filamentous fungi was conducted under the optimal fermentation condition.The biomass of filamentous fungi obtained after fermentation was 12.97 g/L,close to the yield of the small-scale,indicating that the performence of pilot-scale fermentation for biomass production was stable and reliable.?3?Thermo-CaO₂ pretreatment promotes sludge fermentation and improves sludge dewaterabilityThe concentration of volatile fatty acids?VFAs?after anaerobic fermentation of thermo-CaO₂ pretreated sludge reached 7.91 g/L,and the moisture content of the sludge cake after dewatering was only 63.4%,which showed good ability of thermo-CaO₂ in improving VFAs production and the dewaterability of sludge.Economic feasibility analysis showed that the net profit of thermo-CaO₂ pretreatment for sludge anaerobic fermentation was 245.29yuan/ton of dewatered sludge,indicating that this technology has a good application prospect.?4?Pilot-scale study on the improvement of sludge dewaterability by filamentous fungi conditioningCompared with the unconditioned sludge,the moisture content of filamentous fungi conditioned sludge decreased by 14.6%and the filtrate volume increased by 25.0%after dewatering by plate-and-frame filter press,indicating that the filamentous fungi conditioning was effective in improving sludge dewaterability.The filamentous fungi and sawdust showed a good synergistic effect in improving sludge dewaterability,the moisture content of sludge cake was further reduced to 63.7%by the combination conditioning of filamentous fungi and sawdust after dewatering.Waste Aspergillus niger conditioning could also effectively improve sludge dewaterability.Economic feasibility analysis showed that the cost of sludge conditioning with fermentation-derived filamentous fungi Talaromyces flavus S1 was 185.2yuan/ton wet sludge,while the cost of sludge conditioning with waste Aspergillus niger was only 1.7 yuan/ton wet sludge,which was lower than the cost of conditioning with conventional chemical conditioners polyacrylamide?PAM?and polyaluminum chloride?PAC?.This technology showed a good application prospect.