Crocodiles Snap Up Benefits Of Bespoke Wastewater Treatment

• Zoo enhances onsite wastewater treatment for visitors and reptiles
• Bespoke WCSEE HiPAF meets 7m3/day capacity and environmental consent
• Complex requirements, including fluctuating loads, met by partners

A zoo specialising in crocodile conservation has selected an enhanced effluent treatment solution from wastewater technology specialist WCS Environmental Engineering (WCSEE). A planned site expansion, along with drainage challenges, prompted the zoo to install a bespoke, off-mains wastewater treatment plant at its site in Oxfordshire.

The zoo is home to over 100 reptiles, representing 18 species of crocodiles and other reptiles, including the critically endangered Siamese Crocodile from Cambodia, and the world’s largest lizard, the Komodo dragon.

Modular design
To meet the wastewater treatment requirements of the crocodile pools, as well as the seasonal and daily fluctuations of the visitor facilities and onsite restaurant, WCSEE worked with wastewater system specialist Soma Services to design and manufacture a modular HiPAF packaged treatment plant with 7m3/day capacity.

Graham Hyde, sales director at Soma Services said, “The HiPAF wastewater treatment plant is the ideal solution for the crocodile zoo, where the site is not connected to mains drainage and has unique and complex requirements.

“The crocodiles swim in pools operated in a similar way to swimming pools, where filters regularly backwash water, which needs to be treated before the effluent is discharged into the environment. The backwash flows are intermittent, so complex calculations were needed to analyse firstly what needs to be treated, and secondly, how to spread the wastewater load throughout the week to best utilise the HiPAF treatment plant.”

Environmental compliance
Prior to installation, a discharge permit was obtained from the Environment Agency, and following technical guidance from Soma Services, the HiPAF was designed to meet a consent for 20mg/l biological oxygen demand (BOD), 10mg/l ammoniacal nitrogen and 30mg/l suspended solids. A balance tank was installed in front of the HiPAF to control the flow and manage load fluctuations.

The zoo and Soma Services worked closely with landowner Christ Church, University of Oxford, and property agency Savills to repurpose a corner of a nearby field, where the HiPAF installation was completed by June 2025. The site was prepared using a cut and fill technique, where soil was excavated from higher areas and used to build-up lower lying land; creating a level surface and minimising visual impact.

Hyde said, “To match the zoo’s mission of promoting better understanding of crocodiles and to secure their future, it needed a wastewater treatment solution that would meet the zoo’s needs now and for the long term. In line with our dedication to crocodile conservation and public education, it welcomes over 100,000 visitors each year.

“Working closely with all parties involved from initial enquiry to design and installation has ensured that the site requirements, for reptiles and visitors, have been met. It's been a fantastic collaboration, and Soma Services has been present throughout the entire process, helping the zoo to understand how the WCSEE HiPAF works and how it fits into daily operations and site management.”

Biological treatment
The HiPAF treatment process works in three stages, starting with primary settlement. Raw wastewater enters the first tank, where gravity pulls organic and inorganic solids to the bottom, preparing the ‘liquor’ for biological treatment.

A unique forward-feed arrangement uses an airlift pump to move wastewater to the secondary treatment stage. This acts as a buffer, preventing peak flows from entering the system and mitigating hydraulic surges.

Stage two is biological treatment, which involves the circulation of specially designed plastic media in the second tank. These lightweight carriers provide a surface for the beneficial bacteria to grow and treat the wastewater.

Diffusers installed beneath the media bed ensure an even distribution of air to circulate the media, and the HiPAF’s enhanced hydraulics make high-rate processing possible. Segmented process chambers in the biozone eliminate the risk of process short-cuts and mitigate risks associated with variable loads.

Stage three is final settlement, where an airlift pump automatically transfers settled humus sludge back to the primary settlement tank for co-settlement and later desludging. The final effluent is discharged through gravity displacement to either a watercourse or sub-surface irrigation field.

The zoo has plans to expand its site in the future, which may require the installation of a second HiPAF tank and the continuation of the collaboration with Soma Services and WCSEE.

Steve Holt, technical sales manager at WCSEE said, “This has been a truly unique project for WCSEE and is a perfect example of how the HiPAF technology is adaptable to meet bespoke customer needs to ensure wastewater is treated to the highest environmental standards long-term. If the crocodile zoo seeks to expand in the future the team will be on hand to help.”