Water reclamation process options

Chidambara, R. Tan, E.K. et al. 2008. Wash water in waterworks contaminants and process options for reclamation. Journal of Environmental Sciences 20 1300-1305. 

Figure 7.1 shows the two major treatment options to obtain RO-quality water from sewage and seawater. The key in water reclamation is to first treat the sewage biologically and use MF/UF membrane filtration to remove suspended solids. Two membrane filtration alternatives are available for water reclamation tertiary filtration (TF) of the effluent from a conventional activated sludge (CAS) process and an integrated membrane bioreactor (MBR). For seawater desalination, pretreatment must be provided if the source is open seawater. The current practice involves multimedia filtration, but membrane filtration has also been considered. 

The properties of the water are important factors in the success of both dry and wet reclamation options, as is shown in Figure 10.10. The acute and chronic impacts of the process-affected waters on aquatic biota, wildlife, plants and humans exposed to them, are complex and typically require ongoing investigation. The com-... 

The chemical and physical properties of clay suspensions produced during oil production from oil sands are described. With a composition of approximately 70 wt% water (with some unrecovered bitumen) and 30 wt%solids (>90% less than 44 gm in size)9 these clay suspensions consolidate very slowly. Clay aggregate or floe morphology has been shown to be a function of the water chemistry and can be manipulated to produce a tailings suspension that is easier to consolidate and dewater. Commercial oil sands processing has been going on in northeastern Alberta since 1967, and in that time approximately 250 million m3 of this difficult to dewater clay suspension has been produced. The reclamation options for this material (mature fine tailings) on a commercial scale are also outlined. 

However, with ageing, the toxic response per unit of naphthenic acid decreases. From Fignre 38, the reduction in naphthenic acid content and of acnte toxicity with time for tailings waters, stored under aerobic conditions, is evident for an array of biota. Natural bioremediation processes are proceeding in the oil sands extraction waters, once they are removed from fresh input of process waters and maintained under aerobic conditions. This biodegradation process is the basis on which the both the wet and dry landscape reclamation options operate. With time, waters will be slowly released from the varions sinks (sand deposits, fine tails) in the end-lease landscape. If the rate of their release is less than the rate of the bioremediation processes, then the resulting waters should have the toxic components of the naphthenic acid group reduced to levels that will ensure the waters are neither acutely nor chronically toxic [136,142],... 

A problem common to all membrane processes is that posed by the retentate in which impurities are concentrated. In some cases, retentate can be discharged with wastewater. Other options include evaporation of the water followed by disposal or incineration of the residue, reclamation of chemicals from industrial wastewater, and disposal in deep saline water aquifers. For the special case of desalination of seawater by reverse osmosis, the retentate is returned to the ocean, which has the potential to cause problems due to excess salinity. 

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