Try a bespoke solution for your engineering problem
By carefully considering clients' requirements and examining their existing systems, Wehrle Environmental UK is adept at providing individual turnkey solutions across a range of process engineering applications, from landfill to cheese making.
Following detailed site evaluations and pilot trials, it designs processes to optimise the use of existing equipment where possible, and systems can be operated and maintained by Wehrle's staff, ensuring minimised whole life costs.
Landfill leachate poses specific challenges for MBR technology.
High concentrations of COD, ammonia and chloride require a biological treatment system that extensively nitrifies (i.e. oxidises ammonia to nitrite and nitrate) while withstanding corrosive chloride-rich influent.
Wehrle MBR systems are considered best available technology (BAT) under IPPC guidelines across an extensive range of industrial sectors.
Leachate from Sita Suez's Beacon Hill site near Poole, Dorset is treated using Wehrle MBR and NF technology. Here, the local trade effluent discharge consent specifies a strict limit of 625mg/l COD, so on-site treatment using MBR and NF technology was necessary because the leachate influent COD loading can reach 5,000mg/l.
Sita Suez is committed to best environmental practice and operates a comprehensive environmental management system to ISO 14001, which has its own internal quality environmental monitoring system (QEMS).
As principal contractor, Wehrle had to meet stringent QEMS targets set by Sita Suez to ensure the project both met and exceeded regulatory requirements.
Faced with restricted space, located within future landfill void space, Wehrle's system had to be compact yet capable of being relocated in the future.
To substantially reduce COD levels, three biological nitrification reactors in series reduce COD and ammonia levels. Following cross flow UF for biomass solids separation, cross flow NF is used for effluent polishing to reduce residual COD levels.
The whole system was supplied on a turnkey basis with all necessary instrumentation and PLC controls accessed via an integrated HMI system, while Wehrle staff operate and continuously optimise the process to ensure reliability and "consistently excellent effluent quality".
Dairy Crest's facility at Foston had existing wastewater treatment equipment comprising DAF and BAFF systems, with final discharge originally to a local sewer.
The equipment worked effectively but with a planned expansion of processing on site, Dairy Crest knew that additional wastewater treatment capacity would be required to ensure it could exceed its environmental responsibilities.
Following the installation of a Wehrle MBR system at Dairy Crest's Davidstow advanced cheese manufacturing plant in Cornwall, Wehrle was called in to evaluate requirements prior to expansion at Foston. Extensive investigations and pilot trials were undertaken over a three-month period, and the result was a recommendation from Wehrle to Dairy Crest to initially continue using the existing Balance Tank and DAF but with the DAF re-optimised to treat the waste prior to entering a new MBR system .
This was to ensure that total loading to the Wehrle MBR system did not exceed design limits.
Wehrle's system design now allows the direct discharge of the highly treated water to a local river. The specific site objective for the upgrade was to design for an initial increased plant capacity of 650m3/day.
The cross flow UF filtration stage was supplied as a containerised, pre-assembled and tested plant, minimising site work associated with installation and commissioning.
The UF plant incorporates robust tubular membranes with two UF loops, each equipped with six membrane modules.
Membranes are currently fitted to three modules on each loop, providing for the possibility of 100% expansion of membrane treatment capacity in the future. At that stage it will be possible to increase the plant capacity to 1,000m3/day, with the BAFF tank upgraded and converted to an additional bioreactor.
The effective treatment of distillery wastewater has always been important, particularly when copper removal is required.
Chivas Brothers wanted to implement BAT at Glenallachie, near Elgin in Scotland, to ensure it could consistently meet its discharge licence conditions for the local watercourse. Copper levels were also a major priority for Scottish Environment Protection Agency.
Chivas Brothers decided to use Wehrle because the company offered a proven MBR process and was able to design a system that fully integrated with the distillery's existing waste management and control systems.
The new effluent treatment system at Glenallachie has a small footprint, minimal sludge yield and a low environmental impact.
The main process plant is installed inside an existing building with two modular bioreactors located outside. All wastewater on the distillery site is treated by Wehrle's two-stage cascading MBR system, having first been collected in three separate holding tanks.
Foul condensate is diluted with washing water from around the site, spent lees from the second distillation stage is then mixed with this, and the combined wastewater is pH-corrected before being treated by the MBR system.
By carefully designing a two-stage cascading aerobic system, an approach proven by Wehrle on several challenging applications around the world, the process can tolerate the potential toxicity of the influent copper and biodegrade the mostly soluble organic loading chemicals and fine solids to a level suitable for membrane separation through the UF system.
The pH in each bioreactor is controlled to retain the influent copper in its relatively inert insoluble or complexed form. The cross flow UF separates the mixed activated sludge into a concentrated stream (which is returned to the first bioreactor for re-treatment) and a permeate stream of treated water with exceptionally low chemical and solids content.
The copper is effectively retained within the biomass, while treated water is discharged to the local watercourse, meeting the final discharge quality requirements licensed by SEPA.
Road tanker washing facilities at Birrfelden in Switzerland normally generate 30-100m3 wastewater from rinsing out more than 50 Bertschi tankers daily. These tankers are used to transport 6,000-plus types of resins, polymers and other chemicals, resulting in wastewater that is both high in COD and variable (20,000-50,000mg/l).
The wastewater treatment system was upgraded using Wehrle's extensive
international experience, the key treatment requirements being to consistently produce up to 100m3/h final effluent with COD <1,000mg/l. This was achieved while meeting a low specific energy consumption requirement, with Wehrle's design solution incorporating MBR to replace the existing conventional activated sludge plant on site.
Extensive on-site testing was conducted prior to the design of the full scale system using an automated pilot scale Wehrle MBR system.
Trials were compared against physico-chemical and biological treatment alternatives. Wehrle's MBR system proved effective at consistently reducing solids and COD to required levels.
Projected whole life costs were significantly less than the alternatives, and specific energy consumption objectives were readily met.
The Wehrle MBR approach to effluent treatment is becoming the method of choice across a wide range of applications, and it is the only realistic membrane process option for leachate treatment with high COD, ammonia and chloride loadings.
MBR systems can be designed and optimised to treat highly variable COD, remove copper and other chemical contaminants, and reduce high solids loadings.
Wehrle MBR systems are robust and reliable and they produce a much lower solids loading in the final effluent compared to conventional clarifiers. They are also space efficient, being well suited to treatment plant upgrades where space is limited.
The company's approach to solving effluent treatment problems "is unique", as it focuses on understanding the problem and using existing site equipment by undertaking detailed feasibility studies and pilot trials, and it strives to re-use or refurbish existing equipment where possible.
The result is an efficient process solution at an affordable whole life price.
By understanding client requirements over the longer term, additional future capacity can be planned in to allow expansion at a later stage at minimal cost. Systems can also be provided integrated into containers or designed to fit into available space. This brings the benefit of pre-installed components and bespoke design to projects where required.
Proven as BAT in the sectors identified above, the Wehrle cross flow MBR process offers several distinct advantages. The system provides excellent and reliable final water quality, it offers an enhanced treatment performance with a small overall footprint, it results in minimal sludge yield and it has a relatively low environmental impact.
Tony Robinson is at Wehrle Environmental in the UK. T: 01993 849300