Despite its suitability, application of UV light for wastewater treatment is not a novel technology largely used for wastewater treatment. Turbidity and suspended solids present in wastewater have an influence on the treatment efficiency. To overcome this problem and increase the treatment efficiency, it is convenient to place a form of mechanical separation to the treatment train before the UV reactor – such as micro-strainer filtration.
UV light can degrade organic pollutants photochemically by direct and indirect photolysis. During direct photolysis, the pollutants move into an excited state causing the direct reaction of the pollutant with other substances present in water. During indirect photolysis, pollutants react with hydroxyl radicals generated after addition of ozone or hydrogen peroxide in water. Treatment efficiency of UV can be boosted by addition of hydrogen peroxide that is directly degraded by UV light on hydroxyl radicals. The process is called hydrogen peroxide photolysis and hardly degradable compounds such as pharmaceuticals and chlorinated hydrocarbons can be degraded. Photolysis of hydrogen peroxide has an advantage in higher treatment efficiency and lower consumption of electricity at the same time.
The main components of the pilot plant combining micro-strainer filtration and UV radiation are:
A submersible pump is used to pump biologically treated wastewater from the storage tank to the pilot plant. The discharge of the pump is directly led to the micro-strainer filter. The pump is controlled by a frequency converter used for changing the pump speed and hence the flow of the water. Dosing of hydrogen peroxide is ensured by the peristaltic pump in order to ensure uniform flow of hydrogen peroxide. The pump discharge is connected down flow to the UV reactor inlet pipe.
The micro-strainer filter is equipped with steel filter mesh with size 65 μm. The maximum flow rate is 10 l.s-1. Content of suspended solids can be reduced to 5 - 8 mg.l-1.
Downflow the micro-strainer there is homologated UV emmiter installed in a flow-through reactor. UV reactor is equipped with six low-pressure UV lamps, each with 80 W output. UV unit is suitable for flow up to 10 l.s-1 at which the UV dose is approximately 220 J.m2 at UV transmittance 60 %. Each UV emmiter is cleaned by automatic wiping system.
Last object is sharp-crested weir used for measurement of water flow. The weir is placed in the flume and is equipped with ultrasonic level meter for automatic reading of flow rate.
Electric consumption of individual components is measured to allow assessment of electricity consumption and economic evaluation of the pilot operation. The actual flow and total volume of treated water is measured by inductive flow meter. The pilot plant is equipped with automatic samplers placed on the inlet to the pilot plant, after the micro-strainer filter and on the outlet of the pilot plant.