The SOLVOX®-V process combines excellent oxygen utilisation and high oxygenation efficiency rates, together with intensive wastewater agitation. It is more economical than other methods and offers high flexibility for oxygen dissolution and process mixing, especially when integrated with existing aeration equipment.

1. HARNESSING OXYGEN TO BOOST PERFORMANCE
IN WASTEWATER TREATMENT PLANT UPGRADE
Chemical production plants are under mounting pressure to process ever larger quantities of wastewater to increasingly higher standards while also needing to operate under various regimes of cost constraint. Plant operators face the dilemma of how to maintain treatment throughput at reasonable cost even when the plant reaches design capacity. The challenge can be compounded by potential changes to production mixes, which often call for additional investment. However, the often prohibitively high costs of building additional plant capacity to meet the competing demands of throughput and changing production mix can, in many cases, be largely mitigated by introducing the latest wastewater technology to inject new life into the plant, therefore extending useful asset life without heavy upfront capital investment.
Industrial wastewater contains numerous contaminants that require removal including suspended solids, dissolved organics that remove oxygen from water and refractory compounds that do not biodegrade easily and could potentially accumulate in the natural environment. Primary and pre-treatment processes remove solids through physio-chemical actions and a secondary treatment usually involves a biological stage where naturally occurring bacteria are used to breakdown and remove the organic content. The most commonly used process globally is the activated sludge process that utilises aerobic bacteria to breakdown and render harmless the organic constituents of the wastewater. Increasingly, tertiary treatment processes, such as advanced oxidation (O3/UV/H2O2) and Fenton’s reagents (Fe2+/ H2O2), for example, are used to remove biologically inert compounds.
Another key driver requiring chemical companies to consider an upgrade to their existing wastewater treatment plants is ever-tightening environmental legislation. It is widely accepted that industrial concerns cannot wilfully pollute natural water resources and, as part of their permit to operate, these companies must demonstrate that they are able to treat all their pollution streams to national regulatory standards in the countries where they operate.
Linde Gases Division is seeing considerable interest in several technology applications to deliver cost effective solutions for increasing the existing capacity of wastewater treatment plants. This article showcases a highly successful intervention from March 2011 using one of these processes at LG Chemicals in South Korea, one of the largest Korean chemical companies. LG Chemicals manufactures a wide range of products, from petrochemicals to high-value added intermediates and high performance industrial materials.

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When the opportunity arose to increase production capacity at LG Chemicals, the existing air based plant was judged to be unable to meet the future demand for dissolved oxygen in the bioreactors comprising the secondary treatment stage. Without an effective intervention, this part of the process would have deteriorated, resulting in a potential drop-off of in performance, exposing the company to potential regulatory penalties for possible environmental infringements and having an adverse affect of the downstream Fenton’s Reagents tertiary stage. In extreme cases of permit excursions, a company’s license can be reviewed or even suspended until the required improvements are put in place. LG Chemicals’ plant challenges included high-salinity wastewater and operation at elevated temperatures in the secondary treatment stage - recorded as high as 48 degrees Celsius. Another stipulation of the upgrade programme was that all equipment must be installed without interfering with the current plant operation.
When Linde was approached to propose solutions to increase the oxygenation capacity of LG Chemcal’s existing wastewater treatment plant, the company advocated its proprietary SOLVOX®-V process. The SOLVOX®-V process, particularly suitable for oxygen dissolution into basins with low water depths, would increase the dissolved oxygen in the secondary treatment stage. In basic terms, SOLVOX®-V units consist of submersible pumps with a very high hydraulic efficiency factor, a distributor for the division of water with low oxygen content into separate streams, gas/liquid contact venturi pipes for efficient oxygen transfer in the form of very fine bubbles plus mixing nozzles for the even distribution and dispersion of oxygen- enriched water. High velocity jets generated at the outlet of the SOLVOX unit provide re- circulation of the oxygenated wastewater at the bottom of the basin to ensure an ideal rate of oxygen utilisation and efficiency is continuously achieved. The injection of oxygen is automatically controlled by a signal from an installed dissolved oxygen probe via a transmitter located locally to each aeration basin.
SOLVOX®-V units are the result of continuous advancement of existing technologies for oxygen transfer. The performance of biological wastewater treatment for industrial wastewater is generally further enhanced through operating a secondary treatment stage at dissolved oxygen levels above 2 mg/l and this is possible due to the high driving force of pure oxygen and efficient oxygen transfer. The SOLVOX®-V process combines excellent oxygen utilisation and high oxygenation efficiency rates, together with intensive wastewater agitation. It is more economical than other methods and offers high flexibility for oxygen dissolution and process mixing, especially when integrated with existing aeration equipment. Assembly requirements are minimal, with no construction work required and the system is ready to operate within a

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very short time. Assembly is also possible in fully operational tanks, so avoiding the costs and inconvenience associated with a process shutdown.
At LG Chemicals it was vital to ensure the equipment would be suitable for the highly saline, high temperature operating environment and this was achieved this by harnessing a nano- particle, ceramic-based coating and using sacrificial zinc anodes. A frame was also constructed that allowed for the lowering of the equipment into the wastewater without damaging the existing aeration tubes and facilitating withdrawal for planned maintenance.
The necessary equipment was delivered on-site two weeks ahead of schedule and installed and commissioned in two days. No shutdown to normal operations was required as the equipment was installed on purpose-built steel frames into the existing plant and mounted above the existing air-based diffuser system at the base of the tank. Within two days, performance testing confirmed that the process was working optimally and almost immediately LG Chemicals experienced a plant performance improvement in dissolved oxygen. It was possible to reduce the existing aeration system by more than 40% and still achieve the desired operation for the secondary treatment stage. The performance of the secondary treatment stage was improved from around 60% to 70%.
Linde’s intervention focused on the biological treatment phase, removing up to 70% of the pollution load, measured as Chemical Oxygen Demand (COD), after which the wastewater at LG Chemicals passes through several more stages of treatment, most notably a Fenton’s Reagent tertiary stage. Improving on this secondary treatment stage reduces the work required for the downstream processes, as well as the total cost of treatment. The system implemented at LG Chemicals achieved the required outcome without the need to physically build any extra volume capacity onto the plant. Using the company’s existing assets and retaining everything on the same footprint, a technologically advanced but straightforward upgrade was achieved in less than a week.
The controlled input of pure oxygen can help to the overall performance of wastewater treatment plants and offers fast, flexible and efficient solutions for the biological treatment of wastewater.
Linde’s extensive range of SOLVOX® process solutions facilitate aeration by introducing pure oxygen into wastewater in a variety of ways, considerably enhancing the overall capacity and effectiveness of existing wastewater treatment plants. Adding pure oxygen with the SOLVOX®

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process can also increases the process performance of an existing plant, requires a very low investment and can be flexibly adjusted to seasonal needs or production campaigns.
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