[Translate to UK English:] A Case Study: Handling leachate; a full system solution

[Translate to UK English:]

With large landfill facilities come great challenges to the water cycle and local ecosystems. The creation of leachate through the percolation of rainwater and potential run-off creates a hazard, which is required to be processed. A number of facilities are providing this service, all of which with significant demands for handling fo this difficult fluid.

A leading waste and effluent processing company in the Midlands operates 2 large sites, taking in both tree cuttings and woodchip from local services and leachate from landfill sites.

Leachate contains high levels of COD and BOD as well as nitrates, which are hazardous to the environment and needs to be processed as specialist waste. Treatment of leachate by a local water authority is a significantly higher cost compared to treatment at the purpose built facility.

The company operating the site produce multiple revenue streams from the sites:-

  • Charging for treatment of waste (leachate and wood chip)
  • Returning energy to the national grid
  • Producing compost from the processed leachate

[Translate to UK English:] The Process

[Translate to UK English:]

The process begins by the production of steam from the burning of the tree cuttings and wood chip from a boiler, which in turn powers a steam-driven turbine. The turbine provides energy for the entire plant with a surplus being sold back to the grid.

The leachate is offloaded into a series of 100m3 storage vessels. When stored, the iquid will result in settlement as it contains gritty particles and oily residue, with a sludge forming at the bottom of the tank, so it must be agitated within the vessel.

The leachate is circulated within the storage vessels by utilising a Verderhus pump to draw the leachate from the base of the tank and discharge it to the top. As the tanks fill, the pipe system allows the circulation process to be switched to transfer through to one of six evaporators and an adjacent mixing tank. The leachate is circulated between the evaporators and the mixing tank where the leachate is gradually dewatered. As evaporation occurs, more leachate is added to the thickened leachate slurry. The feed of watery leachate improves the fluid handling aspect of the process and the quality of the cake.

The steam from the turbine is circulated through the evaporators, generating the heat necessary to remove the water parts from the leachate to the atmosphere. The cake left after evaporation is then taken for further processing before being turned into compost.

[Translate to UK English:] The Verder Scope

[Translate to UK English:]

Initially, Verder was approached to provide the pumps for tanker offloading, recirculation and transfer of the leachate, however upon reviewing the bid for the full project, the company chose Verder to supply a comprehensive pumping solution from tanker-offloading to evaporator.

  • Tanker-offloading facilities.
  • Leachate storage and handling
  • Rainwater harvesting
  • Leachate mixing and dilution
  • Leachate between the evaporators and mixing tank

 

Verderhus pump technology

The Verderhus range of screw-channel provided the robust technology for the handling of the leachate. The pump is unique in that it operates a hybrid principle of both a centrifugal and positive displacement action. The Verderhus range operates with flow rates of up to 1500m3/h yet can handle solids of up to 160mm diameter and flowable slurries up to 3000cps.

The decision to specify the Verderhus was crucial for a fluid requiring elements of both principles, such as leachate which may comprise water, oily residue and abrasive fine grit at approximately 5% composition.

The hybrid pumping principle is possible due to the screw-channel impeller and cone assembly; unique to this category of pump. The contour and shape of the impeller produces compression, similar to a positive displacement pump combined with an open channel to allow the easy passage of large solids. Towards the discharge end of the impeller the diameter increases and the channel contour steepens, increasing the velocity of the fluid, generating centrifugal force, typical of a radial action centrifugal pump. The cone  shape of the pump casing/inlet housing matches the impeller’s increasing screw diameter, providing a close tolerance to achieve efficiencies as high as 70%. The Verderhus was installed for each stage of the process, which gave significant advantages to the site.

[Translate to UK English:] The benefits of a Verderhus screw-channel pump

[Translate to UK English:]

Increased uptime and MTBF - Leachate contains fine solids which are abrasive to a conventional centrifugal pump, however due to the shape of the Verderhus impeller, there is a ‘dispersive’ effect enacted on the fluid and a reduction in abrasion. This reduces the abrasive wear on the impeller. As the impeller eventually wears, it may be adjusted to maintain the tolerances against the cone casing to prevent efficiency loss. This may be done 2-3 times, which extends the life of thepump and total plant uptime.

Optimised storage and circulation processes – A Verderhus pump was installed for each 100 m3 vessel to provide both transfer and circulation of the leachate. There is the risk to any suspension held in a storage vessel of sedimentation which, can form a thick sludge at the vessel base, preventing adequate suction to the recirculation pump. This may result in overworking the pump, cavitation and even failure. The Verderhus pump provided sufficient agitation to the leachate to negate the need for an additional mixer and maintain a homogenous fluid state. This has the additional benefit of fewer scheduled maintenance inspections and cleaning procedures of the vessel and pipework.

Reduction in costs – The Verderhus provides exceptional service life with difficult fluids such as leachate, which over the lifetime of the pump reduces the cost of spare parts, servicing, energy consumption and downtime.

The pump technology was only part of the scope. The Verder Project team provided the complete fluid handling system including:-

  • Full M&E design and functional specification of the system.
  • Civil requirement including design for the tanker offloading area bunded areas to contain the leachate storage tanks.
  • Pipework, valves and fittings
  • Flow meter, pressure transducer and tank level monitoring
  • Fully automatic control including control panel with HMI interface and actuated valves.

[Translate to UK English:] The result

[Translate to UK English:]

The customer required the site to be entirely automated, with the only manual procedure being the connection of the road tanker to the Bauer coupler on the offloading pump.

The system design and use of actuated valves, flow, pressure and level sensors allow both the transfer and recirculation processes to activate automatically. The tanker offloading area is designed to contain any spills. A tanker drives into a small bunded area (bunded by shallow speed humps forming a bund area), the drainage system in this area features a 3-way valve to allow any fluid in the bund to be contained. During normal operation the 3-way valve diverts to a rainwater sump and during the tanker-offloading process the 3-way valve is switched to a leachate sump. Submersible pumps in each sump allow the return of the fluids to the storage or mixing tanks to assist the evaporation process, ensuring any spillage of leachate is contained from the surrounding environment.

The result for the sites was that the leachate could be processed in the most efficient way. This was due to the pumping solution that allowed the handling of a difficult fluid with minimal wear and longer MTBF than alternative pumping technologies. The sites require minimal operational labour outside of the Leachate offloading and standard maintenance and servicing requirements.