A Review of Textile Sludge Management & Biogas Production through Anaerobic Digestion

Sludge is produced by WWTP/ETPs amount to only a few percent by volume of the processed wastewater, but its handling accounts for up to 50% of total operating costs.
To achieve a sustainable sludge management strategy has become a great concern.

Samples of sludge are made by the textile industry and characterized based on some parameters such as pH, solids concentration, oxygen demand, nitrogen, phosphorus, total bacteria, etc. 

Sludge causes pollution of groundwater and land. The analysis revealed that the sludge is highly polluted potentials, and needed proper treatment before disposal to the environment.

What's the Sludge? 
It can be considered as separate solid particles from textile wastewater treatment. The material is black color due to the contribution of a significant quantity of iron present on it. 

Sludge is generated during the treatment process consisting of coagulation (by addition of Aluminum/iron salts), flocculation, Oxidation, Sedimentation, and liquid/solid separation. 

A recent study by a Professor of JU has shown that the textile sludge of BD doesn't contain any notable heavy metals. Energy consumption has been increasing continuously and to meet up the ever-rising energy demand. 

What's the Anaerobic digestion?

Anaerobic digestion is a  process by which microorganisms break down into biodegradable material in the absence of oxygen.
It can be carried out under mesophilic, psychrophilic & thermophilic conditions. In general, mesophilic anaerobic digestion of sludge is more widely used because of lower energy consumption & higher stability of the process.

Moreover, thermophilic digestion is more efficient in terms of organic matter removal & methane production. It enhances the destruction of the pathogen, weed seed & insect eggs thus enable effluent hygienists on. 

Increased energy requirement may be met by implementing a system allowing heat recovery from effluent & cogeneration with biogas.
Low-temperature thermal pre-treatment(temperature lower than 100 degree Celsius) have been pointing out as an increasing biogas producer from primary & secondary sludge.

Process Flow:
1.Hydrolysis
2.Acidogenesis
3.Acetogenesis4.Methanogenesis

Concept of up-flow anaerobic sludge blanket (UASB) reactor, courtesy by researchgate.

The process of hydrolyzation improves the overall digestion process velocity & degree of sludge degradation thus reducing anaerobic digestion time & increasing methane production rate. It is a rate-limiting step of anaerobic digestion.

In recent years, there have been many successful efforts for the co-digestion of sludge with several other substances such as the source-sorted organic fraction of municipal sludge, confectionery waste sludge from paper industries, coffee waste & grease-trap sludge from the meat processing plant.
Co-digestion of sludge at 70 degrees Celsius may enhance bio-gas production as biogas yield can be 30% higher with pre-treated sludge than with raw sludge. Anaerobic co-digestion may provide several benefits like increased degradation of sludge, more optional moisture, nutrient content & dilution of inhibitive compounds.

Evaluation Process:
The concentration measurement of CH4, CO2, O2, NH4 & H2S in textile sludge can be carried out by using absorption sensors working in infrared & electrochemical sensor lines. The gas monitoring system can be calibrated regularly by calibration gases.

The volume of gas can be measured by the displacement of a syringe piston. Focusing on the process, anaerobic digestion can be used in ETP for mass reduction, methane production, and degradation & stabilization of sludge before final disposal and biogas is a by-product of anaerobic decomposition of organic matter.

Expected Outcome:
If this process can be implemented in rural & urban areas of Bangladesh it could be possible to fulfill the high demand for gas. By using this Biogas generator, authority can produce electricity and thus will be a great contribution to decrease pressure from natural energy resources.

1. Biogas can be a good alternative that can be upgraded to compressed bio-methane gas(CBG) so that it can replace LPG and other fuels.
2. Biogas can be used in household chores, electricity production & even in the industry to replace fossil fuel and it is economically viable & technically possible.
3. It can also be a possible way to reduce greenhouse gas emissions. Natural gas is the most important indigenous source of energy that has been continuously produced & consumed since 1970. About 75% of the commercial energy of the country comes from natural gas. It shows our dependency on gas alone and negligence on other resources.
4. The amount of gas in Bangladesh will not last another 50 years in increasing extraction & demand rate. Biogas can be the next big thing to replace dependency from natural gas alone.
5. Considering Bangladesh’s situation, biogas production from textile sludge could be a sustainable eco-friendly technique.
6. Bio-gas is estimated to have the potential to replace around 17% of vehicle fuel. It qualifies for renewable energy subsidies, and it can be cleaned and upgraded to natural gas standards when it becomes bio-methane.
7. This is also alternative disposal of dung, liquid manure, and bio-waste, while simultaneously harnessing energy—a valuable substitute for conventional fuels. It also helps in the reduction of greenhouse gases.
8. The remaining substrate is used as high-quality agricultural fertilizer, characterized by its neutralized acid, higher pH-value, retained nutrients, and lack of odor.
9. The bio-gas may be applied in direct combustion systems for producing space heating, water heating, drying, absorption cooling, and steam production.
10. A final opportunity exists for the sale of biogas through injection into a natural gas pipeline. The cost of this gas is comparatively less and less maintenance is needed, Bangladesh can adopt this method in Central ETP that can make an alternative power source by producing biogas from separated sludge.

Bibliography:
1.Elsevier
2.Asian J. Exp. Sci., Vol. 23, No. 1, 2009; 95-98<
3.Journal of Pollution Effects & Control,DOI: 10.4172/2375-4397.1000180
4.ScienceDirect
5.https://www.frontiersin.org/
6.https://www.textiletoday.com.

Sakib Al Muntasir

Department of Wet Process Engineering, 44th Batch

Bangladesh University Of Textiles.