Reinhard Seidel, sales engineer for Verder South Africa, talks about the need for wastewater treatment plant designers to carefully consider pump requirements and modern options, using both CAPEX and OPEX studies to determine the long-term viability and suitable of their choices.
Click to download and read the pdf
For water to be utilised without harm it needs to be clean and, the fact is, fresh water is not an infinite resource. In addition, increasing urbanisation places strain on water resources and infrastructure networks across Southern Africa. Fresh water used in industrial and process applications that is not remediated properly before being discharged back into local sewerage systems is also a significant contributor to water pollution, placing further pressure on treatment plants.
All this is being further exacerbated by climate change and extreme weather events, most particularly the devastating impacts of drought cycles. This was plain to see in 2018, when following a three-year record drought (2015–2017) in the southwest of South Africa (SSA) and precipitated by the last El Niño, Cape Town came within days of Day Zero – becoming the first city in the world to run out of water.
Startlingly, the latest monthly Seasonal Climate Watch issued by the South African Weather Service makes tentative predictions extending until August, which currently indicate that another El Niño looms for South Africa from mid-year, which could mean further droughts for the Western Cape with consequent water shortages.
Wastewater encompasses a broad spectrum, including drainage from households, commercial establishments, hospitals, and industries. It also includes stormwater and urban runoff, along with agricultural, horticultural, and aquaculture effluent. Untreated, dirty water gets released into natural water reservoirs, where it wreaks havoc on fish, animals, and crops.
As it currently stands, however, wastewater treatment is not being fully leveraged. According to the UN, approximately 80% of wastewater is released into the environment without being recycled or adequately treated. This increases the risk of contamination to potable and drinking water.
Furthermore, failing to fully utilise efficient wastewater treatment has a deleterious impact on socioeconomic issues, impeding sustainable economic development.
Effectively utilising wastewater is not only essential to environmental conservation and a smart way to address water shortages, but also potentially a resource, from which water, energy, nutrients and a variety of recoverable materials can be garnered. According to the UN Environmental Programme, and the Global Wastewater Initiative, there is
330 km3 of municipal wastewater being generated globally each year. If this wastewater could be managed effectively, the resources embedded in the water could be used to irrigate and fertilise millions of hectares of crops, as well as produce biogas that could supply energy for millions of households.
One of the reasons given why wastewater isn’t treated to its full capacity is the cost associated with upgrading wastewater treatment systems. However, the Environmental Protection Agency in the US notes that this can be mitigated, as plant upgrades can pay for themselves and/or end up saving a plant money.
Wastewater treatment plant design engineers have a huge responsibility and stake in the management of diminishing water resources. When designing new, and upgrading existing infrastructure, they should be very careful of false economy when setting the standard for their pump requirements.
Many factors should influence the selection decisions for plant equipment, but with budgetary constraints, many of these factors are often overlooked. CAPEX versus OPEX studies should be extensive in the planning and implementation of new treatment facilities, as well as in managing and operating existing treatment facilities.
For instance, when upgrading aging infrastructure, new and improved technologies should be explored and considered instead of just replacing equipment like-for-like. The process should constantly be assessed and viewed in its entirety, and ultimately developed, refined and improved by adopting modern and more economical solutions to better the overall plant efficiency and efficacy.
There are technological developments that can help reduce costs associated with maintenance and improve plant uptime, such as peristaltic dosing pumps, which are efficient and cost-effective. Over time, this technology has evolved from familiar lower pressure, low-flow medical devices into heavy duty, medium pressure industrial pumping solutions that mimic the well proven principle of peristalsis found in the human body.
Sometimes called hose pumps, peristaltic pumps are essentially simple, using a specially designed, reinforced rubber hose that is repeatedly compressed by a rotating pressing shoe and then allowed to relax. This action results in a simple positive displacement pumping mechanism with a powerful, high vacuum suction, dry priming action.
A key factor in wastewater treatment applications, is that the pumped medium – for example, lime, flocculant or other dosing chemicals – is always contained within the tube and never allowed to come into contact with any of the pump’s moving parts. There are no valves, glands or seals for the pumped medium to affect, which often account for the weak points on other pump types.
The Verderflex Ds500 peristaltic metering and dosing pump, for example, can handle solids, abrasives, slurries and crystals – and is not affected by ‘off gassing’ of compounds such as sodium hypochlorite in the potable water industry. These features make the unit fit-for-purpose for more advanced wastewater treatment plants.
This brings significant benefits in eliminating much of the process downtime and maintenance costs, as the only component that may need to be replaced with any sort of frequency will be the flexible hose.
Doing so effectively returns the pump to its ‘as new’ condition. In addition, these pumps are cost effective when the entire lifecycle cost is considered and, resulting in lower overall maintenance costs and downtime, they offer a higher return on capital. They use less space and power than other conventional pumps, and they can be operated continuously without any problems, meaning that process operations do not need to be interrupted. The pumps contribute to boosting operational efficiencies and they pose less risk of leakages, because there are no seals to leak, which means less waste and fewer contaminants are released into natural environment.
Data from the EPA notes that some wastewater treatment plants can remove more nitrogen and phosphorus from their discharges than others, depending on the equipment used and how the wastewater is treated. This suggests that there is room for progress and improvement, which bodes well for better and more economical wastewater treatment.
While there are many and complex aspects involved with a circular approach to complete water management, there can be no doubt that successful water treatment of wastewater is essential for the sustainability of water resources and our planet.
