A sequencing batch reactor (SBR) is a good fit for leachate that must have its ammonia and COD reduced, particularly where a temporary or self-contained plant is needed. It treats the leachate in batches in a single tank, so it needs less plant than a continuous system. This post follows a proposal for a temporary SBR at a UK landfill, covering what was supplied, how long installation and commissioning take, and why timing depends on the weather.
The challenge: ammonia and COD in a temporary scheme
A UK waste operator wanted a temporary leachate pumping and treatment plant for one of its landfill sites. The leachate quality objectives were to reduce ammonia and COD (chemical oxygen demand). Ammonia and COD are the two measures that most often drive leachate treatment, because both are typically elevated in leachate and both can be controlled by biological treatment.
Because the plant was temporary, the design had to be self-contained, quick to install and easy to remove. It also had to start working reliably within a realistic commissioning period.
The approach: one SBR and a buffer vessel
The process
The proposal was a single SBR and a discharge buffer vessel, installed in a secure compound on site. Leachate feeds the SBR from existing buffer storage. The SBR reduces both COD and ammonia, and the system produces two outputs: the sludge that collects at the base of the SBR, and the treated leachate leaving the plant.
The equipment
- The reactor: fabricated from glass-lined steel sheet, mounted on a concrete foundation.
- Pipework: UPVC of the kind used for leachate duty, with flanges and valves chosen to match.
- Pump and aeration skid: a single skid carries the pumps and motors that circulate fluids and aerate the SBR. Site pipework conveys fluids and air to and from it.
- Inlet filtration: duplex inlet filters that remove solids down to 3 mm, protecting both the SBR and the pumps from heavy solids and sand.
- Controls: fully PLC controlled, with float-type level switches suspended inside the vessels. Flow meters and on-line analysers were available as extra items.
The controls for the whole assembly are mounted on a single support frame with a rain shelter, on a concrete foundation. Site wiring is done by suitably qualified electricians.
Installation and commissioning: realistic timescales
The delivery and installation figures are a useful benchmark for any similar temporary plant:
| Phase | Typical duration | What drives it |
|---|---|---|
| Installation on site | 4 to 6 weeks | Access, working hours |
| Electro-mechanical commissioning | About 2 weeks | Engineer on site |
| Process commissioning | Within a 4 to 6 week overall commissioning period | Season, availability of leachate |
| Performance testing | After commissioning is satisfactory | Commissioning engineer’s sign-off |
The process commissioning time depends on the time of year, because bacteria are more active in summer, and on the availability of leachate to seed the process. An SBR is a biological system. Unlike a pump or a filter it cannot be started on a fixed date and expected to perform immediately.
Installation follows a clear sequence: review all design parameters, complete the detailed design, prepare the site, mobilise the plant, cast foundations, install the SBR and buffer tanks, then the pump skid and control panels, bring in power, connect pipework and cabling, commission the electrics on water, and only then bring in leachate and commission the process.
Interfaces and exclusions
Some items are typically left to others or priced separately: the power supply to a switch-fused isolator in the compound, a telephone line for telemetry, and ground preparation for foundations (which needs a detailed site survey). Operation and maintenance after process commissioning is excluded unless agreed in writing. Optional services include ongoing operation with full responsibility for performance, monthly or quarterly servicing, and operator training.
Why it works
An SBR combines biological treatment, settlement and discharge in one vessel, which is why it suits small or temporary schemes. The single skid keeps the mechanical equipment compact, and the self-contained compound limits the interfaces with the rest of the site. The key trade-off is that biological systems take time to establish and are sensitive to season and feed.
What to consider for your own project
- Define the objectives. State the ammonia and COD you must reach, and the consent that applies.
- Allow for biological start-up. Commissioning can take longer in winter, and you need leachate available to seed the process.
- Protect the process from solids. Duplex inlet filters allow one to be cleaned while the other is in service.
- Decide who operates it. Make clear whether operation and maintenance are included, or whether your own staff will handle them after commissioning.
- Check the regulatory position. The Environment Agency’s landfill permit guidance is the place to start.
FAQ
What does an SBR do?
It treats wastewater in batches within one tank, using aeration and settlement. Here it was used to reduce ammonia and COD in landfill leachate.
How long does commissioning take?
In this proposal, four to six weeks, including two weeks of electro-mechanical commissioning before process commissioning.
Why does the season matter?
Bacteria are more active in summer, so the process establishes faster in warmer conditions.
What waste does an SBR produce?
Two streams: sludge from the base of the reactor and treated leachate.
Planning a leachate treatment plant?
Share your leachate analysis and consent limits and we will propose a treatment route. You may also want our post on filtering leachate suspended solids.