Salinity and Temperature Effects on Oily Produced Water Treatment Using Polyaluminium Chloride

Abstract

AbstractPolyaluminium chlorides (PAC) has replaced a large part of traditional aluminous coagulants for water treatment in recent years because of low dosage, high efficiency, low cost and convenient usage. This work studied the effects of salinity and temperature on the efficiency of PAC in removing oil and colloids from oily produced water (PW) and the potential of PAC for high salinity PW treatment.Minghua produced water (Di-MHPW) with salinity of 2,815 mg/L and high salinity produced water (HSPW) with salinity of 102,290 mg/L were used in this work. The efficiency of PAC and the optimal dosage were investigated by stability analyzer which allows a step-by-step vertical scanning of the dispersions. The separation time, floc volume and water quality after treatment could be obtained by stability analyzer.Transmission intensity was used to evaluate the oil-water separation in PW. High transmission intensity indicates low oil content. Without PAC, HSPW presented faster increase in transmission than low salinity PW indicating poorer stability. The zeta potential of oil drops and colloids in low salinity PW (2,815 mg/L) was −20.4mV. High salinity (102,290 mg/L) increased the zeta potential to −2.2mV, which makes the oil-in-water (O/W) emulsion unstable than low salinity PW. With the addition of PAC, HSPW results in slightly lower transmission with less floc volume. This could be explained by the floc size after the addition of PAC in two PWs. The size of formed floc in HSPW was much smaller than that in MHPW leading to slower separation of floc from aqueous phase and lower transmission intensity. Increasing the temperature enhanced the PAC efficiency in removing oil and suspended solids in both high and low salinity PWs. However, the floc volume also increased especially in Di-MHPW resulting in less water volume. In HSPW, the temperature effect on floc volume was not obvious. Though high salinity reduces the performance of PAC in water treatment, it is still an efficient flocculant for HSPW treatment with high flocculation efficiency, small floc volume and short separation time.This work provides the insight of oily produced water treatment using PAC and the effect of salinity and temperature. The results are helpful to develop novel flocculants used for high salinity produced water treatment.