Experimental study on low heat-NaOH combined treatment for the release of carbon source from cracked concentrated activated sludge
This study investigated the cracking of residual activated sludge using a low heat NaOH combined treatment method.The effects of NaOH dosage,heating temperature and reaction time on the carbon source released from sludge cracking were studied,and the efficiency of using sludge cracking solution as a re-placement for biological nitrogen removal and carbon source was evaluated by analyzing the total nitrogen removal rate.The effect of this method on the sludge reduction was also examined.The results show that the dissolution rate of SCOD increases with increasing NaOH dosage,heating temperature,and reaction time;the best cracking effect is achieved with a NaOH dosage of 3.0 g/L,heating temperature of 70 ℃,and the reaction time is 24 hours,where the SCOD concentration of the sludge supernatant reaches 1.829× 104 mg/L,and total nitrogen,ammonia nitrogen,nitrate nitrogen,and total phosphorus concentration reaches 943,419,487,and 204 mg/L,respectively.The sludge reduction effect is significant with a decrease in TSS content from 61.70 g/L to 29.25 g/L,and VSS content from 31.95 g/L to 6.95 g/L.The biological reduc-tion effect before and after sludge cracking is very significant;the median diameter size is 30.2 μm and 8.7μm,respectively before and after sludge disintegration and a large number of ultrafine particles with a size of around 0.15 μm were generated.SEM results show that sludge flocs and microbial cells are destroyed.In the denitrification experiment,the sludge cracking solution under the best conditions was used as a supple-mentary carbon source,resulting in a COD utilization ratio of 83.4%and a total nitrogen removal ratio of 60.1%,indicating that the nitrogen removal effect was significant.This study demonstrates the potential of using the low heat NaOH combined method for sludge cracking and reduction,and as a replacement for bio-logical nitrogen removal and the carbon source.The sludge reduction and resource utilization are excellent,which can provide a basis for optimizing the thermal alkali pretreatment of residual activated sludge.