By Mike Bambridge, managing director of CST Wastewater Solutions
Efficient and easily maintained screening is the first and very critical stage in municipal and industrial wastewater treatment, as water industry plant operators keenly appreciate.
WWTP operators are the people who have to ensure that screens and compactors capture floating solids that would otherwise flow through a wastewater treatment plant, potentially causing equipment damage and blockages.
This task is growing more demanding and unpredictable, particularly during times of flood and irregular loads, which are increasingly common in these days and erratic conditions affecting different areas in different ways. The problem is worldwide, but especially prevalent in the notoriously variable conditions of Australasia and the broader Asia-Pacific, where regulators as intensely concerned about water quality, environmental spills and water tables.
Headworks are the first line of defence to help prevent such issues. It is true that pumps and dewatering systems are engineered to handle some impurities and variations, but, beyond a certain level, debris and irregular feeds can lead to equipment failures and faster component wear.
Unless solids are efficiently separated out from wastewater at the start of the purification process, you are inviting trouble into the system. This can cost dearly in terms of downtime, environmental risk, clean-up costs and OH&S hazards for the operator teams involved.
Thus, ease of maintenance of headworks is a key consideration in preventing trouble, especially for municipalities and smaller industrial concerns operating on tight budgets. These entities also do not have the financial resources or large engineering teams to implement complex technologies for wastewater treatment.
Flexibility is also key to ongoing efficiency in handling diverse inputs and flows, regardless of the location and input. Headworks that are efficient over diverse conditions — that do not fail when you need them most, such as under high load or flow — are vital to all the downstream purification and recycling process stages in a properly engineered wastewater treatment plant.
As a result of our experience over more than 30 years of wastewater installation and operational experience throughout the Asia-Pacific region, we have taken a different path to many in producing our different headworks designs for municipal and industrial applications to prepare for a future that is already arriving.
A different approach
Our engineering approach is not one-size-fits-all, because one size (or type) does not. Our horizontal in-channel rotary drum screening technology is built from the outset to be both robust and adaptable, not to be cheaper up front, but to transfer cost and problems down the line.
This whole-of-lifespan value, as distinct from a race to the bottom on sticker price, is a mature engineering approach in meeting and continuing to meet users tasks that vary from place to place, day-to-day and week-to-week as loads on the system change.
Some non-technical people might ask, “So what?”. We are not addressing them. We believe the guys on the front line, the operators and engineers, will have a different view. That’s why we present our engineering and operational principles for a mature and timely discussion.
There are common features we embrace that are universally beneficial to WWTP’s expected to perform and keep on performing.
Compared with typical traditional screening at wastewater treatment plants, for example, our in-channel technology has lower fluid head loss at peak flows to increase solids removal efficiency.
When dealing with fine screening of larger flows, this technology has the advantage of mechanical simplicity, self-cleaning and high efficiency screening. This results in reduced maintenance and cheaper whole-of-life costs compared with other types of screens, such as band and inclined drum screen designs.
Functional layout of CST Wastewater Solutions’ In-Channel Rotary Drum technology
Key to delivering this functionality is the configuration of the design, in which the screening drum is installed horizontally semi-submerged in line with the incoming wastewater. The plate at the back of the drum re-directs flow radially through the mesh to optimise solids separation and self-cleaning.
The rotary drum is manufactured from either self-cleaning wedge wire for primary screening, or perforated plate for fine pre-membrane bioreactor (pre-MBR) screening. It is washed by a system of spray nozzles at a moderate pressure.
Our screening technology approach provides for optimal adjustment of screen gap widths and sieve hole diameters for the most appropriate screening result when matched to individual installations’ characteristics, such as the application flow and local site conditions.
An internal hopper collects the screenings, which are flumed out to the integral lifting and dewatering screw, to efficiently dewater and reduce screenings volume.
The lifting screw is shaftless to avoid any blockages, even in the presence of fibrous products, and includes screen and screening washing. Lifting and screenings handling can also be conducted outside the channel, which increases options for additional washing and dewatering, according to individual applications.
The horizontal drum design lowers operating depth and range to reduce average screen velocities for higher removal efficiencies and easier cleaning than alternative screens.
The benefits of an efficient engineering concept and detailed engineering have combined to produce low whole-of-life costs when compared with most other screens, with servicing required only every four to six years.
The last word
One final way in which we have a different approach is our move to local manufacture closer to the place of use throughout Asia-Pacific.
This move comes as intensifying supply chain issues interrupt, delay and lessen the supply of some of vital waste water treatment technology, which is key to the sustainability and environmental performance of industrial and municipal wastewater treatment plants and key to their overall reliability in delivering services.
Not only does local manufacture deliver a more robust and low-maintenance product — and better whole-of-lifecycle value — but it places the customer next to the source of supply for spare parts, future extensions and retrofits to boost performance long-term.
A heart of stainless steel in the CST Wastewater Solutions wastewater screen drum compactor can withstand shock loads and larger solids while most other screens using lighter mesh construction cannot, causing them to fail prematurely in flood or high variable flow conditions common throughout Asia-Pacific.
The switch to local production also enables us to offer full stainless-steel products with Australasian metals engineering, replacing carbon steel components and further improving corrosion resistance in harsh local environments.