Removal of recalcitrant organics from reverse osmosis reject water as part of a petrochemical wastewater treatment process.
Arvia were approached by one of the world’s largest petrochemical companies who are involved in the processing, production and sales of petroleum refining and petrochemical products.
The company has a refinery in the East of China and was looking to improve its wastewater treatment process to comply with environmental regulations and reduce operational maintenance of their on-site effluent treatment process.
Manufacturing facilities in China are under pressure to reduce water pollution and address their water usage as part of the ‘Water Pollution Prevention & Control Action Plan’, also known as the ‘Water Ten Plan’.
The key objective of the plan is to protect surface and ground water. Heavy polluting industries like the petroleum sector have been the focal point for enforcement. Facilities found to breach specified standards under the new law face significant fines and prison sentences for directors.
The effluent standards for the petroleum refining and petroleum chemistry sectors came into force on 1 July 2015. Specified limits differ depending on the sector and province but are usually between < 50 or < 30 mg/L chemical oxygen demand (COD).
Prior to the enforcement of the Water Ten Plan, some sectors did not have any specified limits for effluent quality. This meant that discharging untreated wastewater into waterways was permitted. This has resulted in facility management requiring the installation of complete water treatment processes from scratch.
Since enforcement in 2015, water treatment technologies have been integrated which in many cases are not advanced enough to reach the specified limits. Arvia has been partnering with companies in China since 2016, offering an eco-friendly and low-maintenance wastewater treatment alternative.
An engineering team from Arvia conducted initial treatability trials at the client’s facility in Nanjing, China on samples of the recalcitrant refinery effluent. This effluent was from a reverse osmosis system (or RO system), which concentrates harmful chemicals into the reverse osmosis reject water, or ‘RO reject stream’.
Using Nyex™ technologies, a Chemical Oxygen Demand (COD) reduction, down to 12mg/L was achieved on the concentrated RO stream, which entered the Nyex™ system at around 60mg/L.
After seeing the trial results, the client went ahead with the purchase of a full-scale Nyex™-a PLUS system to treat effluent at 60m³ per hour at their refinery facility.
The new water treatment system consisted of a set of submergible reactors which, placed inside a large treatment basin, combine adsorption with electrochemical oxidation.
The concentrated RO stream is gravity fed into the treatment basin containing the Nyex™ reactors. Once in the basin, atmospheric pressure drives the water into the base of each reactor and up through a bed of carbon-based adsorbent media. Due to the use of gravity and pressure, there is no need for pumping the water, which saves the end-user additional operational expense.
The carbon-based media inside each Nyex™ reactor localises the harmful organic chemicals onto its surface and these pollutants are simultaneously oxidised using an electrical current. The treated water overflows out of the top of the reactors and is directed out of the basin for further water treatment processes.
The purpose of the Nyex™-a PLUS in this application is to remove the most persistent organic chemicals to protect the biological treatment step which is further downstream. If the chemicals from the RO stream were to react with the biology, this vital water treatment step would be damaged and would become ineffective.
Due to the flexible nature of the Nyex™ process, it can be installed as described here to support other treatment processes. It can also be installed as a final ‘polishing’ treatment step to remove any remaining recalcitrant chemicals from effluent prior to this being discharged.
There are several sites across China owned and operated by this petrochemical company also in need of advanced treatment processes.
Our water treatment specialists work with each site manager on an individual basis, analysing and testing their effluent. This process will ensure that our team proposes the most efficient and cost-effective solution for each site dependent on their effluent quality and discharge targets.
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