Efficiency And Mechanism Of Agricultural Biomass On Improving Sludge Dewaterability

Sludge dewatering is critical to the sludge final disposal process,which is an important part in the whole sewage treatment.At present,the improvement of sludge dewaterability is attributed to the sludge condition applied.Many condition methods are developed due to the diversity of sludge properties.This study investigated three kinds of biomasses which were wheat straw powder(WSP),corn stalk powder(CSP)and rice husk powder(RHP),were used as physical conditioners to improve sludge dewaterability with ultrasonic,sodium persulfate acid and alkali.Their performance and mechanism in improving sludge dewaterability was explored and the new approach in recycling and harmless handling of agricultural waste was exploited in this research.The effects of biomasses on sludge dewaterability under ultrasonic condition were studied.Detecting indexes including capillary suction time(CST),sludge specific resistance of filtration(SRF)were used to evaluate sludge dewatering performance.With an improved SRF test device,sludge SRF could be measured efficiently and accurately.The contents of soluble protein and polysaccharide in the filtrate was used to estimate their interaction degree in sludge condition.Results show that after adding WSP or CSP and processing under 40 kHz ultrasonic for 15 min,sludge dewaterability was improved greatly.SRF reduced from 1.0×109 s~2/g to 0.4×109 s~2/g with dosage of(or more than)0.75g/gDS(dry solid).The sludge cake moisture content decreased from 93% to 80% and from 94% to 79% under a pressure of 100 kPa,respectively,when adding WSP and CSP with 15 min ultrasonic degradation.However,lower enhancement on sludge dewatering performance was observed by adding RHP.In addition,the agricultural by-products would increase the dewatered sludge high heating value,and 15 min ultrasonic could further improve the sludge low heating value by reducing the moisture content.Nevertheless,when ultrasonic time increased to 30 min,sludge dewatering effect became bad,and sludge cake moisture content,CST and SRF increased significantly.The effects of biomasses and sodium persulfate on conditioning sludge were investigated.The results showed that sodium persulfate could significantly reduce the sludge CST and SRF and make CST decreased from 102 s to 56 s,SRF from 1.7×108 s~2/g to 9.0×108 s~2/g when the dosage increasing from 0 to150 mg/gDS.Sodium persulfate also could oxidize extracellular polymer substances(EPS),making the concentration of protein and polysaccharide increased in the filtrate,at the same time,increasing the sludge particle size and Zeta potential.When the biomasses together with sodium persulfate,although CST increased,sludge SRF and moisture content of sludge cake decreased obviously.When dosing 150 mg/gDS sodium persulfate,the corresponding SRF decreased from 1.6×109 s~2/g to 0.38×109 s~2/g,0.36×109 s~2/g and 0.55×109 s~2/g respectively with the dosage of WSP,CSP and WHP increasing from 0 to1.0 g/gDS.Under a low dewatering pressure,the corresponding sludge cake moisture content was reduced from 91% to about 80.0%,79.3% and 81.0% respectively.And the effects of biomass on sludge dewaterability was studied under acid and alkali condition.The experimental results showed that sludge dewatering performance increased at first when pH value decreased from 4 to 2.As pH decreased to 1,the sludge dewatering effect became weak.Alkali deteriorated sludge dewatering effect greatly when pH value was higher than 8,whether the sludge CST or SRF was increased significantly.And the biomass also did not improve sludge dewatering effect,especially at a high pH value.After adding 0.75 g/gDS WSP,CSP and RHP,CST increased to 885 s,916s and 967 s respectively,and SRF increased to 2.7×109 s~2/g,2.7×109 s~2/g and 2.9×109 s~2/g respectively.Through deep dewatering test,finding that biomass improved the deep dewatering performance under chemical or physical interaction significantly.Specially,when dosing 120 mg/g sodium persulfate and 0.5 g/g WSP,the sludge cake moisture content reached to below 60% after deep dewatering.As to the mechanism of biomass combined physical and chemical functon in improving sludge dewaterability,the content of loose bound EPS(LB-EPS),tight bound EPS(TB-EPS),SMP detection,three-dimensional excitation-emission matrix(EEM)fluorescence spectroscopy were applied to reveal the changes in organic material;and bound water used to elaborate the migration of water in sludge;and scanning electron microscope(SEM)showed the changes of morphology characterization,etc.Experimental results showed that the physical and chemical effect reduced sludge TB-EPS and bound water content,in addition biomass formed a skeletal structure to provide water channels,at the same time reduce the compression ratio of sludge,gaining better water-solid separation effect.