Sludge Treatment and Disposal Technology (1)

1. How Is Sludge Classified According to Its Source?

Sludge is a solid sediment produced in the process of water and sewage treatment.

Due to the different properties of various types of sludge, classification is very necessary, and their treatment and disposal are also different. According to its source, it can be divided into:

(1) Municipal sludge (also called sewage sludge), mainly refers to sludge from sewage treatment plants, which is the largest type of sludge. In addition, sludge from water plants also comes from municipal facilities and can be classified into this category.

(2) Pipeline sludge, from drainage collection system.

(3) River and lake sludge, from rivers and lakes.

(4) Industrial sludge, a mixture of solid and water, oil, chemical pollution, and organic matter produced by various industrial production.

In non-specific environments, sludge generally refers to municipal drainage sludge.

2. How Is Sludge Produced From Wastewater?

Wastewater treatment consists of a series of physical, chemical and biological treatment processes:

(1) Sedimentation (with or without chemical flocculants), filtration and purification.

(2) Aerobic and anaerobic treatment by microorganisms to produce organic complexes.

(3) Biochemical denitrification and dephosphorization.

(4) Digestive treatment.

In the process of wastewater purification, pollutants in the wastewater are concentrated and removed through biochemical degradation. Biological treatment can degrade most organic pollutants into water and gas (aerobic treatment produces CO2 and O2, and anaerobic treatment produces gas mainly composed of CH4). Metal pollutants (including heavy metals) cannot be treated and are concentrated in sludge.

Sludge is a solid substance produced in the process of sewage treatment, it is an inevitable by-product of sewage treatment plants.

3. How Is Sludge Classified According to the Sewage Treatment Process?

Sludge from sewage treatment plants can be divided into the following categories according to the different steps of treatment process:

(1) Primary sludge: after physical-chemical treatment.

(2) Secondary sludge: after biological treatment.

(3) Tertiary sludge: after dephosphorization/denitrification.

According to the properties of sludge, it can be further divided into:

(1) Undigested raw sludge.

(2) Digested sludge.

Sludge digestion can be divided into aerobic and anaerobic.

4. What Is Sludge Drying?

The sludge produced by sewage treatment has a high water content. Due to the characteristics of water and sludge particles, mechanical removal has certain limitations. The organic matter content, ash ratio and especially the amount of flocculant added in the sludge have an important influence on the final solid content.

Generally speaking, mechanical dewatering can obtain a solid content of 20% to 30%, and the dewatered sludge is also called mud cake. The water content of the mud cake is still high and has fluid properties. Its disposal difficulty and cost are still high, so it is necessary to further reduce the amount. At this time, in addition to natural air drying, large-scale reduction can only be achieved by inputting heat to form evaporation. The use of heat for drying is called thermal drying.

5. What Are the Economic Parameters of Sludge Drying?

Sludge drying is the process of evaporation of water. In order to conduct a survey on the drying project and determine the scale of the reduction treatment, it is necessary to understand some economic parameters of the sludge project. These parameters include:

(1) The solid content of wet sludge after mechanical dewatering.

(2) The purpose and type of final disposal.

(3) The cheap heat energy that can be found locally and its price index.