Trouble shooting leachate treatment

The treatment efficiency of landfill leachate plants can be enhanced by optimising the method of plant operation, rather than by costly capital investment, argues Manish Pankhania

The majority of landfill leachate treatment plants in the UK are sequencing batch reactors (SBRs). The SBR process is popular because of its relatively low capital and operating cost compared to other treatment processes, and its efficiency at treating biochemical oxygen demand (BOD), chemical oxygen demand (COD) and ammonia.

The treatment process, which typically takes between 10 to 15 days, helps to absorb shocks and, with a period of extended aeration, it generates relatively small amounts of surplus sludge - minimizing sludge handling and disposal requirements.

Over time, many SBR plants start to lose some of their benefits, mostly due to changes in leachate quality and volume and environmental conditions. Consequently, many plant operators opt for expensive plant upgrades in an attempt to return their plants to maximum treatment efficiency.

Recent projects have shown that treatment efficiency can often be restored and even improved upon. The key to troubleshooting a plant is to understand how the biology of the plant works and to exploit this to its maximum. With the right technical skills, the biomass can be made to work much harder and this can avoid the need for expensive plant upgrades.

Consider this case study in which a client operated a SBR leachate treatment plant with a design throughput of 120m3/day of leachate, but never managed to treat more than 60 to 70m3/day. In an attempt to improve the flowrate, they invested in a 290m3 influent balancing tank. The idea was to supply a more consistent quality of influent and reduce shocks to the biomass. However, the balancing tank only increased the throughput of the plant to 80m3/day.

Don't jump to costly decisions
The client was considering a costly upgrade to its venturi aeration system when engineers at SLR Consulting implemented a process audit of the plant. This identified two main areas of the plant's operation that needed to be improved. Firstly, more frequent nutrient addition and monitoring was recommended and secondly, optimisation of the different phases of the SBR cycle - the settlement time, feed and aeration time.

As a result, with the addition of regular desludging and other minor modifications, the flowrate of the plant was increased from 61 to 121m3/day. At the same time there was an improvement in the effluent COD, suspended solids and ammonia quality. This reduced the plant's trade effluent costs. The dissolved oxygen levels in the plant also improved and a £60,000 upgrade to the aeration system was not required.

Key factors for running this plant at maximum efficiency were: to have a good understanding of plant microbiology, leachate treatment processes, optimising the batch treatment cycle and closer plant monitoring. The main costs incurred in this project were increased monitoring costs, transport costs for surplus sludge removal and the purchase of more nutrients.

Dr Manish Pankhania is leachate treatment specialist at SLR Consulting

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