A better solution for sludge drying treatment?

Calcium-added drying technology is a newly developed method for drying, stabilizing and recycling sludge from sewage treatment plants by using additives in China. A two-component heating agent containing quicklime (alkaline) and aluminum ferric sulfate (acidic) was used to dry, dehydrate and modify organic acid decomposed sludge, and then it was transformed into stable inorganic matter. According to the principle that calcium hydroxide is dehydrated into calcium oxide, the additive can be recycled after the treated substance is calcined at high temperature. The purpose of this study is to replace the single-component sludge treatment process of "lime method" abroad with two-component heating agent, so as to reduce the cost of sludge harmlessness.

The calcium enhancer used for sludge treatment is a solid acid-base two-component heating agent, and the basic component of the heating agent is activated quicklime. The main reactions are as follows:

Calcium oxide +H2O = calcium hydroxide+hydration heat release

Ca(OH)2+ organic matter in aqueous sludge = organic calcium salt +NH3 =

The acidic component of the heating agent is aluminum ferric sulfate. In addition to chemical products, slag from iron sulfate pickling and drying in steel mills or other chemical iron removal slag can also be used. The main reactions can be simplified as follows:

Hydration exothermic reaction of Fe2 (SO4) 3+6H2O = 2Fe (OH) 3+3H2SO4+

Hydration exotherm of Al2 (SO4) 3+6H2O = 2al (OH) 3+3H2SO4+

There is also a reaction between the acid and alkali components of the heating agent:

Ca(OH)2+H2SO4=CaSO4+2H2O+ Acid-base neutralization exothermic.

Proper addition can quickly raise the temperature of sludge to above 100℃, and evaporate a large amount of steam in a short time, thus achieving the purposes of drying, dehydration and sterilization. The pH value of sludge treatment can be adjusted by the ratio of acid to alkali, and the added elements are calcium, iron, aluminum and their compounds, which are acceptable for general building materials. Compared with using the same amount of single quicklime, the acid-base two-component heating agent can increase the heat by more than 30%.

3.3 process flow

The sewage treatment scale of Fangzhuang is 40,000 m3/d, and the sludge output is about 20 ~ 30 m3/d (water content is 80%). Sludge consists of primary sludge in primary sedimentation tank, residual sludge after biological treatment and chemical sludge in high-efficiency reaction tank. 3.4 Therapeutic effect

Fangzhuang Sewage Treatment Plant adopts calcium-increasing drying technology to treat dehydrated sludge with water content of about 80%. Calcium-enriched drying analysis showed that the temperature of dehydrated sludge increased rapidly after adding two-component heating agent, and the highest temperature reached 95℃ in 10 minute, and the temperature increased by about 70℃. The test data are as follows:

Table 2 Test Data Sheet

Water content (%) organic matter (%) fecal coliforms

(individual/gram) coliform group

Total number of bacteria (per gram)

(per gram)

Before treatment, A77.8 42.15.0e+051.2e+07 4.3e+08.

Before treatment, B 79.7 42.8 3.2E+05 8.4E+06 5.4E+07.

After treatment, A 28.0 3.28 was not detected, not detected, not detected.

After treatment, B 27.9 7.89 was not detected, not detected, not detected.

After drying, the water content of sludge is about 50%, and the organic components are greatly reduced, which achieves the purpose of reducing water content and organic matter, and at the same time, the sludge can be fully stabilized by intense temperature rise. After stacking and full heat release, the final moisture content of sludge treatment is 20 ~ 30%; Grain meridian