A case for decentralised wastewater treatment plants

Decentralised plants can take the pressure off our ageing water and wastewater treatment plants. Kirsten Kelly speaks to Herman Smit, managing director of Quality Filtration Systems (QFS), about the use of these systems in South Africa.

"Over the past 20 years, due to the skills shortage in South Africa, there has been a push towards centralised water and wastewater treatment plants (WWTPs), as these require fewer technical staff members like engineers, scientists and operators. However, when one looks at the types of problems within the water and wastewater treatment industry today, they tend to be network problems. And centralised water and WWTPs have created a bigger dependency upon network maintenance. With municipalities reporting between 29% and 50% of non-revenue water, it is clear that network maintenance has failed. Water has to be pumped kilometres to its consumers and wastewater has to be pumped kilometres to WWTPs – placing huge pressure on network systems. These problems can be solved by decentralising water and wastewater treatment works,” explains Smit.

Previously, there has been pushback against having WWTPs close to residential areas because of the smell. Presently, however, with the adoption of new technologies like membrane bioreactors (MBR), one finds wastewater treatment plants in the basements of high-rise buildings. These decentralised plants are compact, odour-free, highly automated and able to produce greywater that can be reused.

They can also be deployed rapidly due to their modular structure. Smit believes that decentralised WWTPs need to treat between 200 000 litres and 500 000 litres of wastewater a day.

“If it is below 200 000 litres per day, the cost per kℓ is too high and if it is above 500 000 litres per day, its footprint will be huge and may be construed as an unwelcome, major WWTP in a suburb.

“There will always be a case for centralised WWTPs; decentralised WWTPs are there to take the pressure off the existing infrastructure. Many centralised WWTPs are working over-capacity – there are instances where the plant is difficult to maintain, pumps are constantly breaking down or sewage is running down the streets. Upgrading these plants is extremely expensive compared to deploying a decentralised system, which is mostly built off-site and requires a tiny team on-site for its commissioning,” adds Smit.

Smit mentions the recent report by the South African Human Rights Commission (SAHRC) on the spillage of raw sewage into the Vaal River.

“Emfuleni Municipality conceded that it was responsible for the pollution due to its failing wastewater infrastructure and the Department of Water and Sanitation has pledged to deal with these sewer spillages and upgrade the wastewater infrastructure in the area. This is a typical example of a network failure. If wastewater cannot be pumped to the WWTP, the entire network should be evaluated, and an audit done on the money needed to upgrade and maintain it. Decentralised WWTPs would be a cheaper, quicker and safer option.”

Decentralised plants can also be used while a centralised WWTP is undergoing maintenance.

“Sometimes if a WWTP is under maintenance or is upgraded, it is unable to treat wastewater for a period of time. This means that the wastewater may have to bypass the plant entirely. In these cases, a decentralised plant could be used temporarily,” says Smit.

“Our decentralised WWTPs are more affordable because we believe in localising technology – 70% of materials, skills and content used to create our technologies is local. This drives down QFS’s prices and also helps us in providing far better support,” adds Smit.

New technologies and skill sets Smit believes that a barrier to using decentralised plants may be the use of new technologies and skill sets.

“Unfortunately, you cannot use conventional technologies with decentralisation. Technologies like MBR are not really new anymore – they are established and have been used around the world, even in South Africa at the newly refurbished Zandvliet WWTP, for example. However, the industry seems reluctant to use newer technologies and I think this is because, historically, the skill set needed for centralised WWTPs was mostly civil. Over the last decade, water treatment has become a mechanical and chemical process – the skill set has changed. I think government would rather build bigger, centralised water and WWTPs because they know how to do that; they are stuck on the civil skill set and do not have the mechanical and chemical engineers that are needed for newer technologies. Currently, QFS does not employ any civil engineers – we have process, chemical and electrical engineers.”

Decentralised plants require operators, and QFS is committed to training and upskilling people that can operate and maintain these plants.

“We are always involved in the running of a new plant in the first two years and work closely with operators, improving their skill levels. In the Eastern Cape, we are in the process of setting up a training academy where we aim to train six new operators every six months. This training academy will be at the Kowie River Project, where we are building a desalination, water reuse and wastewater treatment plant. This will provide an ideal opportunity to give operators theoretical and practical training on all three technologies,” says Smit.

QFS has seen an uptake in the use of its decentralised systems.

“There is definitely a lot of interest, and we have deployed a number of plants for both the public and private sector in the last two years. We are focusing on building trust and making sure that people understand what they are getting. Decentralisation is not about reducing what you have – it is about improving what you are getting. And we are providing a cost-effective solution with excellent water quality,” concludes Smit.