Sequencing Batch Reactor technology should be the way forward for wastewater management, says David Stagg of Graf UK
The world of wastewater treatment has become a dynamic, complex, and challenging one. Nutrient neutrality that requires reductions in nitrates and phosphates, reducing ammonia levels in effluent, and carbon dosing are just some of the factors that self-builders need to be aware of.
It is no longer simply a choice between that most basic of wastewater solutions – the cesspool, the ‘happy medium’ – the septic tank, or the ultimate – the wastewater treatment plant.
Now there are choices for wastewater treatment plants too – between conventional flow/activated sludge systems and those employing advanced Sequencing Batch Reactor (SBR) technology.
One of the main differences between these disparate systems is that SBR combines various processes during the treatment cycle in a single treatment zone in a chronological sequence which rules out the need for a clarifier/secondary chamber.
SBR systems operate in batch cycles which generally run two or four times every 24 hours to ensure the treatment process is identical every time. This produces high-quality effluent.
Traditional continuous flow systems operate on a ‘what goes in, comes out,’ basis, so during periods of heavy loading/inflow, the effluent travels through the system much more quickly, potentially reducing the effluent quality.
The technology that SBR uses was implemented decades ago for Scandinavia, where reducing and monitoring phosphate and nitrate levels is common practice. More than 5,000 wastewater treatment systems with this technology have already been installed throughout Europe to meet these challenging discharge constraints, achieving an independently tested 0.4 mg/l of phosphate removal with dosing and 1.6 mg/l without dosing for domestic systems up to 50 population. Denitrification is used to reduce nitrates, achieving 7.9 mg/l.
The SBR process is a modern method for cleaning wastewater. Its operational flexibility and excellent process control opportunities, combined with the need to meet the increasingly stringent environmental discharge standards, means it is becoming the system of choice for well-informed self-builders.
Bespoke designs utilising advanced SBR technology are allowing these informed homemakers to meet requirements for decreasing discharge levels of phosphate, nitrate, and ammonia.
SBR technology can be utilised in recycled and recyclable plastic tanks which are eco-friendly and designed for installation using (depending on the ground conditions) granular backfill, which is not only more cost-effective than concrete but also quicker to install. The system is also cheaper for self-builders to run, with lower power consumption from 0.59 kWh/d which equates to approximately £50 per year, based on a cost of £0.25 per kW.
A SBR system is operated by air power generated by a blower/compressor, which means there are no moving parts or electrical components inside the tank itself. This reduces maintenance and replacement costs and makes for a healthier, more efficient operation.
Depending on the objective, the system can control oxygen levels entering the treatment zone allowing nitrification and denitrification treatment processes, as well as varying the duration, frequency, and arrangement of the cycle phases. The plant can therefore easily be customised.
Another benefit of this more advanced system is it comes with underload detection as standard, which allows it to operate efficiently with up to 75% underload – a benefit particularly for second homes which are often left unoccupied for long periods of time. If the system is likely to drop below the 75% underload threshold, carbon dosing makes up the shortfall, as well as enhancing the treatment performance, to ensure low-odour and even odourless treatment and extended times between tank emptying.
SBR technology also differs to conventional systems in that no growth bodies are necessary, as the SBR process does not require the plastic media which can clog and escape from the tank, polluting the environment.
As an alternative to standard batch cycle timings, SBR systems can also be operated depending on the fill level, according to the inflow. If the system’s “buffer” recognises that only a small amount of wastewater has entered, it can automatically switch to economy mode.
The SBR process gives self-builders much greater control over the treatment process, which can be monitored and adjusted when needed. While it avoids the need for traditional tertiary/secondary treatment (such as reed beds which may become less effective over time and during the colder winter months), advanced tertiary treatment stages, such as UV, chlorination, and specialist sand filtration processes, are possible with the latest SBR technology.
Whatever the treatment processes, it is essential the system is commissioned by trained specialists who should also be responsible for its maintenance and servicing. Some manufacturers offer this service for free, as well as extended warranties on the technology of their SBR systems when the purchaser takes up a service agreement with an accredited service provider.
David Stagg is technical product specialist for Graf UK