Large leachate treatment plant

Challenge

The client operates a large landfill site that can generate up to 300m3/day of high ammonia, BOD and COD concentration leachate. Historically, discharge to the public sewer had been allowed with an unlimited maximum ammonia concentration. Due to increased regulatory restrictions at the receiving sewage works, our client was required to limit ammonia in the discharge to a maximum of 250mg/l, or face having to tanker the leachate for off-site disposal at considerable additional cost.

The client needed assistance from a consultant they could trust to procure a suitable treatment plant that could reliably and cost effectively treat the landfill leachate to a quality that would allow its on-going acceptance into the sewer by the sewerage operator.

Solution

SLR were selected to work on this project based on our client’s previous knowledge and experience of working with SLR and the range of relevant specialists available within the SLR team to deliver the project.

SLR was involved with initial optioneering works (LTP sizing, exploring how the landfills environmental permissions could be amended to benefit the project), design and delivery of enabling works (bulk earthworks), production of a tender pack and management of tendering for the main LTP build, selection of a suitable contractor, HAZOP, design iterations, and delivery of the LTP construction project.

During construction SLR filled the role of Principal Designer under CDM, Owners Engineers representative under an MF/1 contract, and provided CQA engineer roles throughout the build.

SLR’s participation in the project has resulted in a high specification plant that is able to exceed the process guarantees stated in the contract. The plant is designed to run with reduced energy consumption and is capable of both nitrifying and de-nitrifying the leachate supplied in a semi-autonomous fashion so as to reduce the need for operator intervention and maximise throughput.

Impact

During commissioning and testing it was demonstrated that the LTP was capable of a sustained throughput at >120% of initial design capacity with ammonia load treated regularly exceeding the design capacity of 750kg/day of NH4-N treated.

The plant was also able to demonstrate reduced alkalinity consumption and need for aeration to consume COD due to the exploitation of an anoxic mixing phase in the treatment process, significantly reducing the carbon footprint of the treatment process.

As a result of the LTP construction the landfill site is able to continue discharging to sewer under the terms of the Trade Effluent Discharge consent that is now in place with a 250mg/l ammonia limit.