Alderholt Nitrate Neutrality

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Client Needs

Alderholt is a village located in East Dorset that is subject to a significant community development over the next 10 years with up to 3000 new homes to be built.

Proposed housing developments are now required to demonstrate nitrate neutral status through nitrate offsetting or by prevention of nitrate release into the environment. Whilst nitrate offsetting can be achieved through securing agricultural land to take it out of agricultural land use, this requires large areas of land that will be costly to the developer. Furthermore, this still allows nitrates to be discharged into the environment and the additional wastewater generated by the development will still need to be treated.

Therefore, it is important to explore opportunities including effective on-site treatment such as the te-cycTM process to help achieve nitrate neutrality or at least minimise any surplus nitrates that need to be off-set through any alternative mitigation.

For these reasons, a modular te-cycTM wastewater treatment plant has been selected for the Alderholt development due to its excellent nitrogen removal performance, low footprint, and ease of operation.

As the community development is spread over a 10-year period, the modular te-cycTM plant will be constructed in 2 phases; this is made possible by the modular nature of the te-cycTM process. Initially, 2 of the 4 te-cycTM tanks will be built, and in year 5 the remaining 2 tanks will be built.

The Solution

The te-cycTM process has over 500 installations worldwide and has been in continuous development for over 20 years, however most of these installations are for sites with population equivalents greater than 10,000PE.

The modular te-cycTM plant has been developed specifically for small to medium sized treatment works whilst still maintaining the benefits and experience of the larger installations.

In addition, the principle of modular package design means that the plant can be manufactured and tested offsite in the Te-Tech workshop and delivered to site via road transport. This reduces the time on-site and all the associated health and safety risks.

Because the system is modular, if the site becomes subject to growth in the future, additional tanks can be delivered to site and easily integrated into the existing system.

The control panel and MCC is also manufactured in-house by Te-Tech’s panel manufacturing division. This means that the control panel can be connected to the plant at the workshop and fully tested before delivery to site. You can find out more about Te-Tech's Automation, Control and Technology capabilities here.

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Process Description

The te-cycTM process, with over 500 reference sites worldwide, is an advanced cyclic activated sludge process achieving simultaneous carbonaceous, nitrification, denitrification and biological P removal.

The te-cycTM process incorporates an anaerobic selector zone, which suppresses the growth of bacteria that cause sludge bulking and includes internal recycling of the biomass to the main reactor zone to create the formation of ‘macroflocs’. 

Cycle

In the te-cycTM configuration these larger macroflocs form an internal anoxic zone and external aerobic zone and contain polyphosphate accumulating organisms or PAO’s.  On the macrofloc surface, bacteria act to convert ammonia to nitrate whilst the PAO's take up phosphorus from the surrounding liquid. Inside the macrofloc, anaerobic bacteria convert the nitrate to nitrogen gas, which escapes harmlessly to atmosphere.

These macroflocs promote enhanced biological phosphorous removal and very low sludge volume indices and the simultaneous carbon oxidation and nitrification / denitrification in one basin enables shorter cycle times and eliminates the need for a separate denitrification treatment stage. The te-cycTM process provides enhanced phosphorous removal to achieve more stringent phosphorous effluent values without the need for an additional solids removal treatment stage.

The process is broken down into three distinct phases that operate on a cycle:

fill/aerate – flow enters the aerated zone from the anaerobic reactor, aeration is controlled by the OUR control system and a portion of the sludge is constantly recycled to the inlet of the selector.

settle – the inlet to the basin is closed, the aeration and internal recycle is stopped and the sludge aggregates as a blanket and settles to the base of the reactor basin.

decant – a moving decanter removes approximately one third of the reactors clear treated effluent, the decanter has an integral scum guard to prevent any floating solids from discharging.

The te-cycTM process incorporates advance process control by means of OUR (Oxygen Uptake Rate). The OUR real time control (RTC) system determines the time and intensity of aeration according to the degree of pollution in the wastewater, ensuring efficient operation of the plant and reduced operational cost.

Small footprint

Process security & resilience

No requirement for primary or tertiary treatment

Low suspended solids

Single stage treatment

Nitrate & Phosphorous removal

Low chemical consumption

Ammonia removal

Low whole life cost

Resistant to flow & load fluctuations / toxic shock

Project Details

Alderholt Key Features           

Population equivalent    7,180

Average Daily Flow          1,077 m3/d

Max Flow Rate                  90 m3/hr

BOD                                     431 kg/d

SS                                         503 kg/d

Total P                               12.9 kg/d

Total Nitrogen                  57 kg/d

Design Temperature        10 °C

Treatment Performance

BOD                                     ≤ 10 mg/l

SS                                         ≤ 20 mg/l

Total P                               ≤ 0.3 mg/l

Ammonia                           ≤ 3 mg/l

Total Nitrogen                  ≤ 10 mg/l

Nitrogen Removal            80%

Tank Details

Number of Tanks             4

Total Tank Volume           2,560m3

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