Characteristics of backwash recovery water from filter for oilfield produced water-suspended solids

The characteristics of suspended solids in backwash recovery water (BRW) from external scrubbingwalnut shell filter in the ‘gravitational sedimentation and filtration’ water treatment process (WTP) for produced water in an oilfield are analysed, then the influence of BRW on WTP efficiency is discussed. The results show that there are a lot of amorphous powder particle flocs or clusters with the diameter from several microns to several tens of microns in produce water, and the amorphous powder particle flocs or clusters are deformable and compressible, they are flocculated and compacted to form larger flocs or clusters under the force of hydraulic pressure in the filtration process while during the scrubbing process, some of these larger flocs or clusters are unable to be separated to small particles. So, in the process of ‘filtration and backwashing’ the small suspended solid particles are aggregated or even coalesced to form larger flocs, which can be removed through gravitational sedimentation, but there is still a considerable amount of small suspended solid particles recycled back to filter through recovery of backwashing water. Recycling rate for suspended solids is 38.5%, which causes a decreased removal rate from the filter. The removal rate from filtration for suspended solids is 59.1% apparently, and 36.4% actually. So, the treatment efficiency of WTP is lowered with unqualified outlet water. This work provides technical support for the operation of the oilfield filter and produced water treatment and provides strong help for the selection of the filter material and backwashing mode of oilfield produced water.