New Possibilities in ETP Sludge Handling and Disposal Methods
By Umesh Kulkari
Cost of sludge treatment and disposal is about half of the total cost of wastewater and sludge treatment and disposal cost. Hence it needs expert attention.
Only few years ago, dewatering ETP sludges to below 20% dry solids content seemed to be impossible. But with the recent advancements, it is possible to get solids as dry as 35 to 40% dry solids.
ETP sludge in any form is hazardous. The hazard is probably proportional to the square of the water content it has at the outlet point. Type of the industry producing the sludge is also very important in deciding the hazard. For example, bio sludge produced from pharma, pesticide and fertilizer industrial segment is far hazardous than municipal bio sludge. Water content in the sludge depends primarily on nature of sludge itself. It also depends upon the practices and equipments used for the purpose. Sludge, broadly is classified as biological or chemical. With the rapid industrialisation the classification ceases to be so simple. Further with global warming outcry becoming shriller by every passing day, it becomes even more important to have a holistic approach.
Many of the pollution issues, which may seem insurmountable, can in fact be solved with will, holistic and focused approach.
Changing the process, using alternative biodegradable chemicals, waste minimisation audits, etc., are some of the tools to ultimately bring about a qualitative difference in the pollution scenario. However my focus through this article is ETP sludge dewatering. I will cover dewatering techniques and final disposal methodologies including incineration.
The main objectives of sludge dewatering are:
- To avoid human contact with the sludge to the maximum possible extent
- To produce sludge suitable for disposal
- For easier sludge handling
- To reduce trucking cost
- To reduce incineration cost where applicable
- To reduce cost of bulking agent in composting where applicable
- To reduce leachate production at land fill site
- To reduce litigation costs
- To carry out these processes without causing nuisance or offence
Following are some of techniques used for sludge dewatering
- Sludge drying beds
- Filter presses
- Centrifuges
- Vacuum filters, and
- Belt filters
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