Economic Development and Environmental Sustainability
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2015 10th Issue: Comparison of Seven Kinds of Sludge Disposal Technologies

All kinds of craft characteristic to the core technology, the main process mainly for seven kinds of sludge disposal, for now, rely on one single process, has been difficult to meet the requirements of sludge disposal.

The main process sludge disposal:

1. Anaerobic fermentation

2. Aerobic sludge composting

3. Sludge incineration power generation

4. Sanitary landfill

5. Rotary kiln drying

6. Plate and frame filter

7. Solidifying agent

Core technical characteristics of a variety of process, for your reference.

A. Sludge anaerobic fermentation

Description: Requires three phases: anaerobic hydrolysis, fermentation and methanogenesis. The first phase, hydrolysis, transforms the particulate matter into soluble compounds. The second stage, fermentation, is the precursor to methane formation. The third stage, methane production, uses acetic acid to splitting methanogens to produce methane and hydrogen.

Disadvantages:

1. Large investment, high operating costs and safety issues.

2. Sludge needs to preheat, which uses a lot of heat, and cannot  maintain itself.

3. It produces a large amount of residue, which needs to be treated again.

4. Methane gas is difficult to incorporate into the municipal pipe network.

5. The northern region wonĄŻt operate in the winter.

6. There are significant safety risks.

At present there are more than 50 domestic anaerobic plants, 29 of which have ceased operations.

B. Aerobic sludge composting

Description: the factory uses straw materials to decrease the sludge moisture content to 60%, then increasing the gap until it reaches a predetermined CN ratio, continuing to replenish oxygen, and fermenting humus for 25 to 30 days. Once stabilization is achieved, it can be used for landscaping and land reclamation.

This process mainly includes: natural compost, closed compost, roller compost, vertical multi-layer compost, etc.

Disadvantages:

1. Mud shale instability, difficult to stabilize heavy metals, can only be used as landscaping fertilizer.

2. Composting process produces a large amount of gas, and pollutes the surrounding environment.

3. Adding a large amount of straw and other conditioner agents to provide oxygen, costs more than 200 yuan/t or more to operate continuously.

C. Sludge incineration and power generation

Description: core equipment incinerator, the main equipment looks like a tower, a perforated plate placed over a plate placed for combustion heating medium sand bed, a tower with refractory lining, gas fed from the bottom, sludge entering into the boiling state of fluidized combustion.

Disadvantages:

1. Large investment, serious corrosion of boiler, high maintenance costs.

2. Sludge with 80% moisture content has low heating value, and consumes lot energy, blending 1 tons of multi-purpose standard coal 70 kg, high running cost 300-400 yuan/t.

3. The emissions impact is big and it is easy to produce harmful gases such as dioxin.

D. Sludge sanitary landfill

Description: Domestic mixed with landfill waste, construction of a landfill site.

Disadvantages:

1. Costs 50 to 60 yuan/t,

2. May pollute a water source or the air

3. Covers a large area of land,

4. Poses a safety hazard

5. At present our country does not have enough land for landfills, the future of sludge landfill is not promising.

E. Rotary kiln drying

Description: Energy such as coal or natural gas is used to analyze the sludge drying dehydration.

Disadvantages:

1. High energy consumption, high operating costs 300 yuan/tons.

2. High temperature drying can produce an odor.

3. The drying process of dust requires strict control, as it poses a safety hazard.

E. Plate and frame filter

Description: Sludge will be diluted by about 90%, then after adding a potion, it is filtered a second time.

Disadvantages:

1. The moisture content can only be 75-65%.

2. Adding a lot of agents increases the sludge dry weight, and results in higher operating costs of around 180 yuan/t.

3. There are limitations for sludge recycling.

F. Solidified agent

Description: Add lime and other curing agents to the original sludge and release a large amount of heat that is generated during the chemical reactions, which will reduce the moisture content.

Disadvantages:

1. Must add lime, aluminum-based material, sludge increment.

2. Sludge cannot be used again, and can only serve as landfill.

3. It has high operating costs of around 130-150 yuan/ton.

While relying on only one of these processes, it has been difficult to meet the requirements of sludge disposal. Depending on the region and types of sludge, comprehensive considerations of the climate, regional characteristics, construction conditions, etc, the ideal choice is to use a unique combination of the various process  in order to achieve the best effect.

On the choice of sludge treatment technology, there is no best choice, only the most suitable choice.

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