The Alum Sludge Reuse report is a resource for Australian water utilities. It provides a detailed examination of opportunities for recovering alum sludge produced as a by-product of water treatment plants in Australia. A wide range of cost-effective alternative technologies were explored as part of this project.
The Challenge
Large quantities of alum sludge are produced as a by-product of alum use as a flocculating agent in the drinking water treatment processes. The question of how to cost-effectively deal with this alum sludge is important as it is used widely by water utilities around the world. In Australia, the cost of alum is low and the used alum sludge is largely regarded as a waste product rather than a potential resource opportunity. As a result, much of it is disposed to sewer or to landfill. This practice has associated financial and environmental costs. Costs associated with transport and disposal of sludge are slowly increasing. Environmental impacts from water treatment plants are being more closely monitored and regulated to improve waste management practices.
To better understand the feasibility of avoiding future costs and to encourage environmental outcomes, options for alum sludge recycling and reuse was investigated.
The Project
The “Alum Sludge Reuse Investigation” was undertaken by a collaborative research team from GHD and the Victorian Centre for Sustainable Chemical Manufacturing (VCSCM)/Centre for Green Chemistry (CGC) at Monash University. Funding was provided by Smart Water Fund as well as ACTEW Water (now Icon Water) and Seqwater.
The project scope examined the current fate of alum sludge produced by water treatment processes in Australia, and the feasibility of a wide range of approaches through which this sludge could be cost-effectively reused, recycled, or put to beneficial applications. New technological solutions from beyond the water sector were explored for the potential to offer innovative solutions and facilitate more sustainable and efficient reuse.
Current use of alum was explored as was the financial and environmental costs involved in its use and disposal. Alternatives for alum sludge end-use were then identified and reviewed, with those end-uses considered broadly applicable across the industry regarded as priorities. Finally, a process was developed to review various sludge recovery methods, treatment and reuse options and compare the relative cost and benefits of each option.
The Outcomes
The final report is of direct benefit to water utilities that use alum in drinking water treatment. It developed an assessment approach that rationally examined different potential end uses for alum sludge and allows comparison of relative costs and benefits of each option. Using this approach, financial and environmental analysis of alum sludge recovery and reuse options was completed. Key outcomes from the project were that:
- there is unlikely to be a single optimal and universally-applicable way to recover and reuse sludge as local factors heavily influence options
- sulphuric acid digestion of alum sludge , for reuse on-site was evaluated as being the most likely to be a cost effective recovery and reuse option for the water industry, and recommended as a bench-scale investigation
- the major opportunities for recovery will be at existing water treatment plants where acid digestion and extraction technology could be retrofitted
- the greatest benefit is likely to occur where capital expenditure for new treatment plants could be reduced through cost avoidance or where local restrictions on sludge disposal were envisaged
- further examination of this process at pilot-scale at an applicable plant is recommended for more accurate and specific estimation of financial feasibility
- operational costs of alum recovery would be slightly higher per unit production rate at smaller plants than larger plants.
