How to Achieve Low Ammonia Levels With MBBR Treatment

Elena Torresi is a Sales & Process Engineer at Veolia Water Technologies. She specialises in the process of designing biological treatment for municipal projects based on MBBR and hybrid technologies. Elena recently presented an insightful webinar for us and here she provides a summary of the session. 

The problem with ammonia

The discharge of a  water source with high concentration of ammonia can have a negative impact on the environment. Aside from causing eutrophication and hypoxia in the recipient water, it can also affect the pH of soil and damage leaves if used as irrigation. In some extreme scenarios, certain natural habitats can even be lost, which has a knock-on effect on wildlife and the food chain. 

As such, more stringent ammonia legislation is imminent. In the UK, there is an upcoming asset management plan (AMP) period, which will require all wastewater treatment plants (WWTP) to have an ammonia target of at least ≤ 3 mg/l in their effluent. As such, it is crucial that WWTP operators are able to effectively and reliably reduce levels of ammonia, which can be carried out through the process of nitrification.

What is MBBR?

MBBR (Moving Bed Biofilm Reactor) treatment is a biological aerobic wastewater treatment process that utilises active nitrifying biofilm growing on carriers made from virgin or recycled High-density polyethylene (HDPE). Each of these carriers has a large surface area on which the bacteria can grow under optimal process conditions. Aeration ensures that the carriers are constantly kept in motion, allowing the bacteria to break down the organic material and the ammonia present in the wastewater. 

Key challenges and considerations 

When looking to implement a water treatment system for the removal of ammonia, there are a number of considerations that need to be made. Firstly,  nitrification rates depend on the concentration of ammonia targeted in the effluent – the lower the targeted level of ammonia, the lower the nitrification rate. As such, in instances where the influent has a low level of ammonia, but not low enough, the technology will require a larger footprint to accommodate the low ammonia rates. 

There may also be circumstances where there is a prolonged low level of ammonia going to the tertiary technology. As a result, it will be difficult to develop and maintain the nitrifying bacteria. 

Conversely, a peak flow event such as a storm can cause the ammonia level to be two to three times greater than normal. Therefore, the treatment technology has to be robust. It will also need to have a good control strategy in place to deal with the peaking events. 

Advantages of MBBR

MBBR technology can provide an effective solution to these challenges. In order to manage the low nitrification levels, the biofilm carriers have a high surface area, allowing the nitrifying biomass to grow. This ensures the system runs efficiently, allowing a compact design. 

Control of the aeration system can also provide the solution to peak ammonia loads. When ammonia levels are high, a higher quantity of oxygen can be delivered into the tank, which in turn will increase nitrification capacity. Conversely, when ammonia load is low, aeration can be lowered, minimising energy costs.

MBBR has several other advantages. Thanks to its simple design, existing MBBR systems can easily be upgraded to increase plant capacity by addition of extra media.

It is also a downstream solution that has a minimal upstream impact because it is independent from sludge recirculation. Therefore, there is no need for a recirculation pump or SRT control as in conventional biological systems. 

Finally, all the activity occurs on the media, meaning there is low solids  concentration in effluent from the MBBR process. Therefore there is often no need to incorporate solid separation after the MBBR (if there are no stringent suspended solids consent) .

Case studies

VWT UK has pioneered the implementation of the technology in the UK with multiple success stories. 

In the first ever UK application, MBBR technology was added to a plant that consisted of two primary settlers, three trickling filters and two humus tanks. The objective was to lower the ammonia level of the plant’s effluent from 15 to at least 3 mg/l and total suspended solids (TSS) from 40 to 15 mg/l. 

Several solutions were considered (including conventional activated sludge) and a tertiary MBBR process with discfilters was finally chosen as the optimal solution. . The resulting plant achieved a significant reduction in ammonia, with the 95%ile ammonia level of the discharge consistently below 0.8 mg/l for the following four years. 

Following this operation, VWT UK built on the knowledge gained and implemented a second MBBR system between 2016 and 2017. As with the first project, there was a need to improve nitrification capacity in order to reduce effluent ammonia levels down from 2.6 mg/l to below 1.2 mg/l. 

Again, this project was successful following the implementation of an MBBR tank. There was no need for filtration on this occasion as influent solid levels were low, with the effluent averaging below 1mg/l, despite multiple peak overloads. 

Since VWT UK’s first MBBR plants were commissioned in 2012, there are now nine new tertiary plants within the UK, each of which have achieved an ammonia level of between 5mg/l and 1mg/l, with further plants being delivered in 2022 and 2023. 

More recently, VWT UK used MBBR technology in a very different application, to clean the runway runoff water at Heathrow Airport. 

In 2019, an MBBR plant was installed at the airport for the removal of glycol - a toxic chemical often found in the antifreeze solutions used on aircrafts, which can be damaging to the surrounding environment. Glycol is rich in biochemical oxygen demand (BOD) and so in this case the MBBR plant would be used to tackle both BOD and ammonia in order to reduce the glycol content in the effluent.

The finished Heathrow plant consisted of two patented AnoxKaldnes™ MBBR tanks, each holding up to 900,000 litres of water. Every hour, 720,000 litres of this water is processed through the plant, removing 550kg of BOD per day. As such glycol levels are significantly lowered, allowing a safe release of effluent back into local water courses. 

MBBR technology offers a proven solution for the removal of ammonia, BOD and other organic contaminants. At VWT UK, our team of experts can ensure that the right combination of MBBR and other water treatment technology is specified and installed to best suit each individual situation. 

Following specification, our team can continue to offer support to ensure that the plant runs as efficiently as possible.

To view the entire webinar and fine out more about MBBR technology, please visit: www.veoliawatertechnologies.co.uk/webinars/demand-webinar-achieving-low-ammonia-levels-mbbr-treatment