## 2 Centralized Treatment Plants
### Industrial Wastewater Remediation
#### 2.3.2 Refinery, Gas and Oil Industry  
Fossil fuel extraction produces water heavily contaminated by organic and inorganic compounds, including different recalcitrant pollutants. To date, the application of a single technology has not been successful in meeting the required quality parameters for water reuse or disposal. The most significant advances have been possibly improving the combination of different methods in sequential and/or combined ways, as recently reviewed by [PERSON] et al. [82]. The key challenge for RO membrane application, fouling, is frequently attributed to the soluble organics and/or field chemicals. Optimizing the correct treatment sequence is complicated at full scale, and studies like that of [PERSON] et al. can be helpful in identifying the best-performing strategy. The key process parameters and the water quality were compared between the bench and full-scale systems to gain insights on RO membrane performance and rejection capabilities. A detailed organic contaminant characterization was used. Process water (PW) was treated in a nutshell filter and then in an MBR, passing through an activated carbon filter (ACF) before reaching the RO membrane, and no fouling was observed in multiple cycles of bench-scale testing, since ACF removed >50% of hydrophobic organics. In the absence of ACF, a 10% decline in RO permeabilityoccurred. Bench-scale operational and water quality results were found comparable to the full-scale plant data, indicating, in this case, the validity of the bench testing protocol implemented to mimic the full-scale system. The reported protocol may be used to optimize a different full-scale WW treatment train, including testing new membranes, different RO recoveries, new membrane cleaning protocols and/or pre-treatment steps [83]. The petroleum refining industry requires copious volumes of water for operation, and water used for cooling can comprise as much as 90% of the total. PW showing high levels of COD, BOD, total dissolved solids (TDSs) and total hydrocarbon content (THC) can be remediated by UF and RO technologies after separation of oil from WW. At an onsite pilot plant, the treatment of real refinery stripped sour water by RO removed 98% of phenols and recovered 90% of the initial water volume to be used in the refinery cooling tower. Hundreds of thousands of m\({}^{3}\) of primary water withdrawal and wastewater discharge can be saved per year in cases the treatment is applied on an industrial scale. Only the management of the concentrate stream can require particular attentions [84]. A flat-sheet RO pilot plant, installed on the treated WW streamline, performed the same remediation process, and the reclaimed water complied with Italian national limits for discharge [85]. However, the water quality parameters for reuse in the same productive site were stricter than those for discharge, and RO effluent was treated by commercial seawater or brackish water membranes. Both were able to reduce contaminant levels well below the threshold values for recycling water to the cooling system. The permeate showed ammonia nitrogen content below 1.1 ppm, total hardness below 8 ppm, Fe below 0.04 ppm and COD below 45 ppm. Moreover, it was ascertained that the flat-sheet membrane configuration was less prone to fouling than the traditional spiral-wound one [86]. An effective, easy to handle and implement technology for removing hydrocarbons from industrial wastewater, a combined approach of absorption and biodegradation, has been applied at a pilot plant to obtain treated water with sufficient quality to be reused in fire defense systems. The plant consisted of four vertical flow columns (bioeractors) made of stainless steel of 192.4 L volume, and each bioreactor included a holder to contain the absorbent material (Pad Sentec polypropylene) with the capacity to retain a high number of hydrocarbons and create a stable microbial biofilm with strong degradation ability.