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Weathering the storm with chemical pre-treatment for wastewater

Stormwater flows can present big challenges for wastewater treatment plants (WWTPs), with huge water volumes needing to be processed in a very short space of time. Kemira has years of experience supporting operators around the world with Chemically Enhanced Primary Treatment (CEPT) solutions that help operators to tackle acute stormwater flows efficiently and cost-effectively without any major investments.

Weathering the storm with chemical pre-treatment for wastewater
Extreme flow, no CEPT Extreme flow, with CEPT
Surface load (m/hour) 8,5  8,5
BOD removal rate <25% 50%
Suspended solids removal  20% 79%

 

CEPT, also known as pre-precipitation, is a simple and cost-effective option for stormwater treatment. Unlike many alternatives, CEPT does not require WWTPs to invest heavily in new infrastructure. CEPT is ideal for increasing the treatment capacity of a plant in storm-flow conditions because it is not subject to the limitations that impact biological treatment, namely the water’s level of suspended solids and flow rate.

During storm conditions, the amount of wastewater flowing into a plant increases dramatically, potentially overwhelming the hydraulic capacity of the biological treatment process. In this situation, incoming flow can be treated with a CEPT process in order to maintain the plant’s ability to effectively treat all the incoming water. Some water will by-pass the biology but all water will be treated.

“CEPT has proven itself in countless studies and customer reference cases over the years,” says Bengt Hansen, Manager of Application Development at Kemira. “It’s a very effective and economical way to reduce the organic load on the downstream biological wastewater treatment process – or even bypass it completely. What’s more, it’s also highly effective at removing phosphorus, which can cut a plant’s energy consumption and therefore its CO2 footprint.”

How it works

CEPT is a process solution used in primary settling tanks to improve the removal of impurities. Coagulant and flocculant chemicals are added to the water before it is fed to the settling tanks. The coagulant helps to bring together the smaller, non-settling solid particles and dissolved substances like phosphates, while the flocculant binds these coagulated particles into bigger flocs that settle easily.

The strength and settling rate can be adjusted by manipulating the chemistry; for stormwater treatment rapidly settling, high strength flocculant is required, and this is where working with an expert partner like Kemira really pays off.

“To achieve good results with CEPT, it is important to identify exactly the right coagulant and flocculant for the process in question but also find the optimal dosing point and appropriate dosing techniques,” Bengt explains. “Our approach is based on working closely with the customer right from the beginning. We’ll hold regular meetings to discuss test results and how to finetune things like the dosing points and amounts, based on our intimate knowledge of the customer’s specific treatment process.”

When it comes to handling stormwater flows, it makes little sense to invest significant resources in a facility that will be used infrequently. CEPT is an effective, flexible, low-investment option that takes up little space at the plant.

The low capital investment choice

Kemira has been offering CEPT solutions for stormwater treatment for many years, with notable projects in both the US and Europe. One of the most recent examples is a project with Stockholm Water, where with Kemira’s help, the customer is able to maintain overall capacity and ensure the quality of wastewater treatment during an upgrade at one its two WWTPs – without the need to invest heavily in infrastructure.

“Biological treatment represents a huge investment for a WWTP and has a very large footprint. Extension of the biological treatment is not only costly but could also be challenging for WWTPs located in areas where space is restricted,” Bengt highlights.

“When it comes to handling stormwater flows, it makes little sense to invest significant resources in a facility that will be used infrequently. CEPT is an effective, flexible, low-investment option that takes up little space at the plant,” Bengt continues. “In a nutshell, all it requires is a few storage tanks and some dosing equipment and piping for the coagulants and polymers – plus of course a healthy dose of application expertise.”

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