Ultraviolet/persulfate pre-treatment for organic fouling mitigation of forward osmosis membrane: Possible application in nutrient mining from dairy wastewater

The forward osmosis (FO) membrane process has recently established its potential as an alternative option to traditional membrane processes for producing clean water and recovering nutrients from anaerobically treated wastewater streams. However, organic fouling of membrane leads to reduced flux, and, thus, reduced amount of the extractable resources. In this study, the impact of ultraviolet/persulfate (UV/PS) oxidation pre-treatment for the mitigation of organic fouling in the FO process during processing of anaerobically treated dairy effluent (ATDE) was determined using a multi-cycle filtration method. The UV/PS performance was compared with control pre-treatments such as stand-alone ultraviolet (UV) irradiation and potassium persulfate (PS) oxidation. Size exclusion chromatography confirmed that flux reduction over successive filtration cycles was due mainly to the humic substances and building blocks i.e., sub-units of humic substances in the feedwater. Although all investigated pre-treatment options mitigated membrane fouling, UV/PS achieved a greater enhancement in flux and decrease in both reversible and irreversible foulant deposition than stand-alone UV and PS pre-treatments. This was because UV/PS could generate sulfate and hydroxyl radicals, which were effective for decreasing the bulk organic content and fluorescent organic content, and particularly for breaking down the large molecular weight (MW) hydrophobic compounds to small MW hydrophilic components, resulting in less organics adhesion to the membrane. This research shows the applicability of UV/PS pre-treatment for the organic fouling mitigation of FO membrane during processing of ATDE for applications such as nutrient mining from ATDE

Extraction of strategically important elements from brines: Constraints and opportunities

Strategically important elements are those that are vital to advanced manufacturing, low carbon technologies and other growing industries. Ongoing depletion and supply risks to these elements are a critical concern, and thus, recovery of these elements from low-grade ores and brines has generated significant interest worldwide. Among the strategically important elements, this paper focuses on rare earth elements (REEs), the platinum-group metals and lithium due to their wide application in the advanced industrial economics. We critically review the current methods such as precipitation, ion exchange and solvent extraction for extracting these elements from low-grade ores and brines and provide insight into the technical challenges to the practical realisation of metal extraction from these low-grade sources. The challenges include the low concentration of the target elements in brines and inadequate selectivity of the existing methods. This review also critically analyzes the potential applicability of an integrated clean water production and metal extraction process based on conventional pressure-driven membrane and emerging membrane technologies (e.g., membrane distillation). Such a process can first enrich the strategically important elements in solution for their subsequent recovery along with clean water production

Mining phosphorus from anaerobically treated dairy manure by forward osmosis membrane

We investigated the effect of draw solution type on the forward osmosis (FO) performance for enriching nutrients from anaerobically treated dairy manure (ATDM) followed by chemical precipitation for phosphorus recovery as struvite crystal. The FO membrane significantly rejected COD (\u3e97%) and phosphate (\u3e98%) whereas there was only 70%-73% and 73%-76% rejection of ammonia-nitrogen and total nitrogen, respectively. The draw solution type had little impact on the retention of the aforementioned wastewater constituents by the FO membrane. At 60% water recovery, a water flux decline of 82%-96% was observed due to increasing contaminant concentration in the concentrated feed solution. Water flux decline was less for MgCl2 than EDTA-2Na and NaCl as draw solutes. On the contrary, the reverse solute flux was higher for NaCl than MgCl2, which in turn was higher than EDTA-2Na. Pre-concentration of ATDM by FO facilitated struvite precipitation. MgCl2 as the draw solute provided a higher purity of struvite than EDTA-2Na and NaCl. This is because when MgCl2 was used as the draw solute, the reverse salt flux of magnesium to the concentrated ATDM provided favourable conditions for struvite crystal formation. This study demonstrates the technical feasibility of phosphorus recovery from ATDM using the FO process

Biofiltration of feedwater to control organic fouling of low pressure membranes

The application of low pressure membrane (LPM) technology, i.e., ultrafiltration and microfiltration, for drinking water treatment and secondary effluent reclamation has increased rapidly over the past two decades. A major drawback in the use and operation of LPM processes is fouling due to the deposition of organic matter present in the feedwater on the membranes which leads to reduced water productivity necessitating membrane cleaning, process downtime and eventual membrane attrition. Pretreatment of feedwater using biological processes (particularly slow sand filtration and biological activated carbon) has been investigated as a simple and cost-effective means to control organic fouling of the membrane. In this paper, membrane fouling by the organic matter in drinking water and secondary effluent, the mechanisms of biological treatment systems, and the effectiveness of biological processes for fouling reduction are reviewed. It has been demonstrated that biological processes have great potential for controlling the organic fouling of membranes