How Proper Sludge Handling Reduce Sludge Disposal Cost up to 75%?

Sludge handling is part of wastewater treatment process. The sludge treatment process aims to reduce the moisture content of the sludge as much as possible. Best performance of sludge treatment process will produce low water content of sludge and minimum environmental effect. The slurry will be treated by dewatering machine to generate sludge cake. The moisture content of sludge cake after dewatering process usually around 80 %. Moisture content of sludge cake can be reduced through drying process by sludge drying machine. Sludge cake that has been treated by drying machine has 10 – 30 % moisture content. Low water content of sludge will reduce the cost of sludge disposal.

Sludge Handling Management

Sludge is the residual that accumulated in wastewater treatment. The suspended solids from wastewater that has been treated will sediment and accumulated to be sludge. Sludge is classified to primary sludge and secondary sludge. The primary sludge is generated from chemical process, while the secondary sludge is generated by biological process. The sludge should be treated before being discharged.

Sludge can affect the environment severe than wastewater. Some reasons are:

• Sludge containing concentrated pollutant
• Sludge containing high water content
• Sludge containing new pollutant that produced from chemical treatment to break down the pollutant compounds from wastewater

According to Peraturan Pemerintah No. 85 Tahun 1999, sludge from wastewater treatment that classified as Toxic Hazardous Materials (B3) are:

1. Primary Sludge: Sludge that produced from sedimentation tank. It is containing stable biomass organic compound that easily evaporate
2. Chemical Sludge: Sludge that produced from chemical process in wastewater treatment e.g coagulation – flocculation treatment.
3. Excess Activated Sludge: Sludge that produced from activated sludge treatment which containing organic compounds.
4. Digester Sludge: Sludge that produced from biological treatment both aerobic or anaerobic digester.

Sludge Treatment

The purpose of sludge handling is produce sludge with high solid content or less volume and stable. There are some methods to gain the sludge with low water content such as:

1. Sludge Thickening

Sludge thickening is the process to reduce the volume of sludge by removing the amount of water. In general, the sludge that produced from this process are containing 1-4 % of suspended solid. There are 2 common systems that usually used for sludge thickening. Those are thickening system by gravity and thickening system by floatation.

2. Sludge Stabilization

Sludge stabilization is the process to reduce the organic compounds and microorganism. The purpose of sludge stabilization are stabilizing the sludge and preventing the odor of the sludge before being discharge to the environment.

3. Sludge Dewatering

Sludge dewatering is the process to reduce the water after thickening process. There are various system in dewatering process depends on the types of dewatering machine. Selecting the right type of dewatering machine is the key to optimize dewatering process. A variety of different dewatering machines are widely available for sludge treatment such as screw dewatering machine, filter press, belt press, dry bed and decanter. Belt press and decanter have some disadvantage such as low capacity, noisy and consumable parts. Disadvantage of filter press is long idle time and working in batch system. Nowadays, screw type dewatering machine is widely used in industry due to simple operations, automatic system possible to run 24 hours, low energy and its durability.

• Screw Press

This machine is equipped with mixing tank to mix the sludge and flocculants. The flocculation process is important to make sure the floc-form is formed properly. The floc-form goes to filter main part. The filter main part is formed by a screw axis with fixing and moving plates overlapping. It dewaters adequately by the gravity and the power from back pressure plate during the process. The filtrate water comes out from the space between fixing and moving plates. The sludge cake is discharged from the discharge outlet.

The screw sludge dewatering machine can be run 24 hours with automatic self-cleaning system. The water will spray automatically to clean the fixing and moving plates from the sludge that did not formed properly. The spray can be managed for how long the idle time for spray and how long the spray is running for one cycle.

The electricity usage of the machine is low due to the small motor requirement. Besides, the noise and vibration are very less. The overlapping of fixing and moving plates is not resulting the noise.

• Continuous Filter Press

This machine can be used to the industries that avoiding the chemical for its process. The industries such as food & beverage industry usually avoiding the chemical for its process. The purpose is produce the sludge with food grade. The mechanism of this machine is using air pressure for hydraulic that used to give pressure to the machine. The sludge is supplied to the compartment of each filter. The pressure will push the compartment of filter until the water dropping through the fabric. Disadvantage of this system is doffing time and manpower. Doffing is taking much time. This continuous filter press is available to solve those problem. This filter press running continuously and in automatic mode, so that can reduce the doffing time and manpower.

4. Sludge Drying

Sludge drying is the process to reduce water content of sludge cake after dewatering. This process can reduce a big amount of water from the sludge. The product of this process containing 10 – 30% water content depending on the requirement and the characteristic of sludge. There are various type of sludge drying system that widely used in industries, such as:

• Rotary Dryer

Rotary dryer is divided into rotary drum dryer and rotary wing dryer. In the rotary drum, sludge will be turned by lifting plates. Then, sludge will be uniformly scattered and make full contact with hot air. In order to achieve good pre-drying, sludge can be further dispersed. After pre-drying, sludge will enter pulse air drying tubes through negative pressure at drum’s terminal for second drying. Then, dried sludge will enter sludge collector and be discharged by discharging valve. Drying process is finished. Exhaust gas will enter biomass dust collector through exhaust pipe and fan. These exhaust gas will be evacuated.

Rotary wing dryer can be used to produce dry fine powder and moist granular sludge. There are 3 separate zones set in the drying system. Central retention zone decides the residual moisture and physical size of final products. 

• Hollow Paddle Dryer

Hollow paddle dryer is a continuous indirect heating device for drying the sludge. There are two parallel rotary shaft inlaid with interlaced paddles in the jacket shell. Each shaft is inlaid with hollow fan-shaped paddles staggered at a certain interval, and the shaft rotates at a low speed. Sludge is continuously supplied from the supply port. The heat medium enters the hollow rotary shaft and paddle through the rotary joint installed at the end of the rotary shaft. After heat transfer and drying, it is discharged out of the machine through the rotary joint. Heat medium will also be introduced into the jacket.

• Low Temperature Dryer

This system is using the humidification mechanism of low-temperature heat pump, the sludge cake on the net strip is dehydrated and decremented by way of convective hot air drying. Where the whole system is designed fully closed, and the drying hot air is free from thermal loss. The mechanism of dehumidification heat pump is using a refrigeration system to cool the wet air from the drying chamber and dehumidify, while recovering the latent heat of water condensation to reheats the dry air, which is a combination of dehumidification (dehumidification drying) and heat pump (energy recovery) and is the recycling of energy in the drying process.

How PETRA TEXTIMA Helping Industries in Sludge Handling?

Sludge handling is one of the important stage in wastewater treatment. In accordance with our company concern that always strives to provide solution, we already helped many industries by supplying machineries/chemicals and assisting the industries to solve the problems of sludge handling. Various industries have ordered our machines and services such as textile industries, chemical industries, food and beverage industries, pharmaceutical industries, palm oil industries, meat processing and many others.

1. Textile Industries