| Currently, a major problem faced in the process of sludge treatment and disposal is that sludge moisture content is still as high as 80% after conventional conditioning and dewatering. Sludge moisture content can’t reach the subsequent treatment and disposal requirements. Thus, sludge needs further deep dehydration. However, the sludge deep dewatering agents commonly resistant to degradation, it is easy to bring a number of other problems while addressing sludge dewatering.Considered from the whole sludge treatment process, this topic is designed to exploit the advantages of easily degradable of organic acids. In order to achieve low moisture content of sludge, sludge is pretreated by organic acids to meet the requirements for subsequent processing. This paper studies the content of four parts: The first part is the contrast sludge dewatering effect of several common organic acids pretreatment. The second part is the effects of organic acids pretreatment on the heavy metals in cake and the TOC, TN content of supernatant. The third part is the impact of organic acids pretreatment process on sludge deep dewatering. The fourth part is the mechanism of organic acids pretreatment on sludge deep dewatering. Specific results are as follows:(1)Sludge pretreated by five kinds of organic acids, its depth dewatering performance improved significantly. After 0.1mol/L-0.6mol/L concentration of glacial acetic acid, lactic acid, citric acid, oxalic acid and tartaric acid pretreatment, the cake moisture content is reduced to 68.1%-75.5% while raw cake is still as high as 80.2%. In five kinds of organic acids, after 0.2mol/L of oxalic acid and tartaric acid pretreatment, moisture content of sludge cake is 68.1% and 68.3%, respectively.(2)It is possible to remove part heavy metals in sludge and increase TOC and TN content of supernatant while improving sludge deep dewatering with organic acid pretreatment. After 0.6mol/L tartaric acid and oxalic acid pretreatment, the removal of zinc in sludge cake is 63.1% and 72.1%, respectively; TOC content of the supernatant increases from 49.8mg/L to 27280mg/L and 14970mg/L, respectively; TN content increases from 16.5mg/L to 39.5mg/L and 93.1mg/L, respectively.(3)In the optimal dosage conditions of oxalic acid, temperature, stirring time, stirring speed have little effects on the extent of sludge dewatering. After changes of temperature, stirring time, stirring speed, the p H of sludge mixture is in 1.9-2.1, moisture content of dewatered cake is 59.2%-61.2%. With the improvement of oxalic acid dosage, sludge settling properties, cake moisture content, C/N ratio and the mixture p H values, and t proteins, polysaccharides, TOC and TN content, C/N ratio in the supernatant changes obvious. After 0.34g/g DS of oxalic acid pretreatment, sludge 90 min sedimentation rate increases from 11.3% to 40.4%, moisture content of dewatered cake reduces from 73.8% to 59.2%, C/N ratio in dewatered cake increases from 6.4 to 6.9, the p H of the mixed decreases from 7.0 to 2.1. Sludge concentration in the range of 1.5%-9.5%, the moisture content of sludge cake increases from 58.9% to 76.3%, the p H of mixture increases from 1.7 to 4.7.(4)Mechanism found that charge neutralization of oxalic acid and sludge particle surface charge plays a major role in improving the depth dewatering performance of sludge. When oxalic acid dosage is 0g/g DS-0.57g/g DS, the p H of mixture reduces from 7.0 to 1.6, Zeta potential changes from-13.2 m V to + 4.1m V, d50 reduces from 54.6μm to 50.1μm. From SEM figures shows, compared with the original sludge, after 0.34g/g DS oxalic acid pretreatment, sludge particle structure becomes very dense, The distance of particle is short and EPS in sludge surface significantly reduces. |
