Microbial sludge treatment technology for sewage solutions

1、Removal of heavy metals  

Most of the heavy metals in sludge are in the form of metal sulfide, carbonate, phosphate, iron manganese oxide and organic matter.  Under the action of eosinophilic bacteria, the metal sulfide becomes soluble metal sulfate. At the same time, the insoluble heavy metals in the sludge can be dissolved into the liquid phase by acidification of the medium, and then the purpose of removing the heavy metals in the sludge can be achieved by solid-liquid separation.

2. Improve sludge dewatering performance  

1). Microbial substitution effect  

In the process of bioleach reaction, the bioleach microorganism will completely replace the activated sludge bacteria in the original sludge.  The bioleached microorganisms were mainly autotrophic bacteria, while the activated sludge was mainly heterotrophic bacteria.  The ubstitution of bacteria has the following effects:  

① As the smaller bacteria completely replace the larger bacteria, the original bacteria die or stop metabolism, so the original capillary water and other bound water will be easy to release into free water, so after biological leaching treatment, the sludge can be further concentrated by gravity decanting part of the water.  

② After the replacement of the heterotrophic bacteria in the original sludge by the smaller autotrophic bacteria, the extracellular polymer (EPS) secreted by the former is much less than the heterotrophic bacteria in the original sludge, so the sludge dewatering performance is greatly enhanced.  Because EPS is hydrophilic, the more it is produced, the more difficult it is to dehydrate the sludge.

 2. Bioacidification effect  

In biological leaching treatment, the pH of sludge can be reduced to about 4.0 in biological leaching tank because microorganisms will oxidize the sludge or a small amount of S added exogenously, and hydrolysis in the medium will lead to a decrease in sludge pH. The decrease in pH means an increase in concentration.  The increase of positive charge will neutralize the negative charge on the surface of sludge particles.  As a result, the Zeta potential on the surface of sludge particles tends to 0 from negative potential (-30 ~ -50mV), which is electrically neutral.  Therefore, the sludge particles will not repel each other because the surface is not charged, which is conducive to sludge aggregation and dehydration.  

3. Other effects  

The metal elements in the sludge, especially iron, are oxidized into flocculating minerals after the action of bioleach and leaching microorganisms, and a small amount of secondary minerals such as hydroxyl ferric sulfate, jarosite and Shi's mineral are further hydrolyzed, which have certain contributions to sludge dewatering.  The formation of minerals may have a certain neutralizing effect on the Zeta potential of sludge, and the mineral density is relatively high, which is conducive to the compaction and precipitation of sludge. Moreover, minerals can be used as the frame support of sludge flocs to form a permeable rigid lattice, so as to change the sludge dewatering performance.