Fast response to urgent need for a wastewater solution

Mobile water treatment solutions can help refineries protect their licence to operate and reduce their environmental impact when a rapid response is needed.

Dominique Tassignon
Mobile Water Services (MWS)

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Article Summary

Petroleum refining and petrochemical industries unavoidably generate large volumes of wastewater and are increasingly looking at ways to improve the efficiency and reliability of the treatment of wastewater produced by their industrial sites. There are many environmental and economic reasons to do so, including:
• Environmental protection
• Compliance with local discharge standards
• Lower water supply costs by reusing treated water
• Reducing reliance on scarce freshwater supplies
• Overall optimisation of the water footprint

Effective industrial wastewater treatment is crucial to returning wastewater to the source. However, industrial processes can produce effluents that are challenging in terms of their volume, variability, and composition. Petrochemical wastewater, specifically, contains a broad group of chemicals derived from petroleum and natural gas.

During refining, the water that naturally occurs in crude oil must be removed and disposed of, along with the water used throughout the conversion process. The water from each refinery unit in each stage of the conversion process contains varying but typically high levels of suspended solids, oil and grease, heavy metals, and organics (generating high COD & BOD loads), and high bacterial and viral loads that require specific treatment. Additional challenges may come from a huge range of micropollutants that could also be present.

Treating petrochemical effluent is complex and depends very much on the kind of load and the nature of the process generating the wastewater stream. It can, however, generally be done in several stages. The first is pretreatment of potentially high loads of suspended solids, oil and grease that would be problematic in the following steps by filtering, clarification or air flotation. The next stage involves treating specific pollutants such as heavy metals or organics compounds by physicochemical or biological processes. The final step is polishing the treated effluent before discharge or reuse, using, if necessary, ultrafiltration and/or reverse osmosis, depending on specific quality objectives It is thus critical to assess the physical and chemical characteristics of the effluent to determine a cost-effective and efficient process for petrochemical wastewater treatment.

Temporary mobile wastewater treatment solutions
Plant operators face many other challenges. Worker and expertise shortages, the high footprint of fixed wastewater treatment plants, and tightening budgets make it difficult to present a strong case for capital investment. The fallout has been a reluctance to invest in wastewater projects where the lifetime and return on investment (ROI) are limited, if not non-existent.
In light of this, one of the attractions of mobile water services is their flexibility, as the rental payments can be covered by the operational budget, removing the need to raise capital. Mobile water service suppliers are often willing to enter into pay-as-you-go, multiyear contracts, which help to improve financial planning thanks to predictable, regular payments.

Mobile plants
A lot has changed since mobile water services were first introduced into the market. Originally, they were simply ion exchange resins mounted inside trailers, which could be transported on industrial sites to provide a temporary supply of high purity water. However, customer needs have diversified, generating a demand for a broader range of available physical and chemical technologies for not only process water but also industrial wastewater applications. These technologies include disc filters, multimedia and activated carbon filtration, sand-ballasted clarification, and air flotation with preliminary coagulation and flocculation, and recycling (UF/RO systems).

MWS’s mobile dissolved air flotation series, for example, can be used as pretreatment upstream of a biological plant to remove biodegradable fats, TSS and fibres. These assets can also act as a clarification plant downstream of a biological plant to remove light sludge particles not captured by secondary decanters or perform tertiary treatment.

A typical mobile plant (see Figure 1) may consist of two or three assets or skid-mounted systems, which can be assembled in a plug-and-play fashion. The containers’ portability enables them to be positioned to make the best use of the available space, eliminating or reducing the need for building infrastructure to house the equipment. Any number of assets can be operated in parallel or series, and their modularity allows additional components or treatment steps to be added for extra functionality or increased throughput, even if it is only needed for a short period. Storage tanks and pumps can also be provided – together with interconnecting fixed pipework or flexible hoses, water metres and fittings – and mobile generators support a standalone setup.

These units are characterised by their high standardisation level, which can significantly reduce development, assembly, and commissioning costs. However, each unit must be tested prior to site mobilisation for calibration and, in some cases, must be adjusted for good integration into the operator’s wastewater treatment process system.

Case 1: First aid solution in an emergency situation
A temporary wastewater treatment system is a preferred solution in a crisis, such as a potential wastewater spill or an unsatisfactory operation resulting in the treated water not meeting the specified limits.

At one of the UK’s leading waste and resource management companies that can receive wastewater from hydrocarbon processing operations, rainfall run-off from the company’s landfill site is collected in a lagoon and tested for contamination before being safely discharged into the local watercourse. Leachate, which all landfill sites produce, is collected by road tanker and taken to the local sewage treatment works for disposal. 

The wettest recorded winter resulted in the run-off lagoon becoming full. The high rainfall also generated more leachate than usual, contaminating the lagoon. Faced with 40,000m3 of contaminated water that could not be discharged onto the watercourse, the customer contacted MWS. Its reverse osmosis technology included pretreatment filters to treat the contaminated water to a quality suitable for direct discharge to the watercourse.

The concentrated reject stream from the reverse osmosis plant was tankered to the sewage treatment works, but the volume was reduced by two-thirds, reducing tanker movement, minimising environmental impact, and saving money on tankering costs. “We could only manage four tankers a day at this rural site, and that would take nearly a year to empty the lagoon if we had no more rain. We had to reduce the volume; therefore, mobile reverse osmosis technology was the most suitable option,” said the leachate treatment manager.
Emergency hire equipment offers immediate enhancement to effluent treatment, helping companies achieve compliance and offering them the breathing space to plan a permanent fix. Mobile water service providers can indeed bridge a gap for operators with a problematic wastewater plant until it can be replaced or repaired or even bridge a time period if there are variations in the effluent quality.

Case 2: Keeping refinery online during DAF repairs
At a refinery processing over four million tonnes of crude oil per annum, nearly 70% of the crude oil is used for fuels production, including jet fuel that supplies almost every flight departing from Hamburg airport and heating oil for 250,000 homes in Northern Germany. The refinery is also a chemicals company, manufacturing some 450,000 tonnes of petrochemical products per annum.

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