Pilot investigation for meeting the Dutch water quality requirements by applying tertiary treatment steps
An industrial customer of EPAS International is operating a pilot system of a sequential batch reactor (SBR). This system is operating very stably after several months of operation, but the effluent does not meet the required discharge limits.
The chemical oxygen demand (COD) limit is exceeded (>500 mg/l) and the water is strongly discouloured.
Therefore, EPAS International was contacted to investigate ozonation and the AC treatment separately and combined as post-treatment steps to obtain the required water quality.
Purification with Ozonation
The pilot trials conducted by EPAS International showed potential for the application of ozonation as a treatment step after the SBR. The COD content was below the water quality limit at an ozone to COD weight ration of 4 and a maximum COD reduction of up to 90% was measured during the entire experiment.
Moreover, the water colour disappeared as the ozonation experiment progressed. Ozone will break down and split these compounds, resulting in the removal of the undesired colour, as can be seen in the picture above.
EPAS International has a wide range of activated carbon types at its disposal, making it easy to compare each brand and type of activated carbon (AC), and to select the optimal type for a specific wastewater composition. AC Is easier to integrate into an existing process than ozone, however, its applicability depends on the wastewater composition. Jar tests were performed, where multiple brands/types of AC were tested at various concentrations. Afterwards, the most suited type of AC was selected.
That AC type was then placed in a test column in a subsequent test phase in order to better simulate the conditions that occur on full scale. A high COD removal of up to 92% was achieved, and the colour was removed, but the generated effluent was less transparent than the effluent produced after the ozonation test.
Ozonation in combination with activated carbon
Increasing the ozone ration implies an increase in the energy consumption. It was therefore investigated whether working with a lower ozone dose in combination with activated carbon would lead to equivalent or better COD removal at lower operating costs than one of the technologies applied on an industrial scale. An additional COD-removal of 61% was achieved when treating the ozonated water with activated carbon.
Ozonation and activated carbon were both able to achieve the required removal, but the estimated operational costs for each technology as such were very high, even when combined. Both treatment methods are usually applied as a tertiary treatment or as a polishing step, efficiently removing residual hardly biodegradable compounds, but at much lower COD concentrations. Therefore, EPAS International advised the customer to consider pre-treatment options and to further optimise their existing SBR.