Adewale Giwa

Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities

Oily wastewater poses significant threats to the soil, water, air and human beings because of the hazardous nature of its oil contents. The objective of this review paper is to highlight the current and recently developed methods for oily wastewater treatment through which contaminants such as oil, fats, grease, and inorganics can be removed for safe applications. These include electrochemical treatment, membrane filtration, biological treatment, hybrid technologies, use of biosurfactants, treatment via vacuum ultraviolet radiation, and destabilization of emulsions through the use of zeolites and other natural minerals. This review encompasses innovative and novel approaches to oily wastewater treatment and provides scientific background for future work that will be aimed at reducing the adverse impact of the discharge of oily wastewater into the environment. The current challenges affecting the optimal performance of oily wastewater treatment methods and opportunities for future research development in this field are also discussed.

A critical review on recent polymeric and nano-enhanced membranes for reverse osmosis

In this paper, current and recent advances in polymeric and nano-enhanced membrane development for reverse osmosis have been reported in terms of membrane performance and fouling. Graphene, zeolites, carbon nanotubes, silica, silver, and titanium dioxide are the predominantly tested nanoparticles in current and recent investigations. Membranes from graphene, zeolites, and carbon nanotubes have all been shown to enhance membrane water permeability. Silica has been observed to exhibit high affinity for water and improve the hydrophilicity of RO membranes. Silver and titanium dioxide have strong antimicrobial properties and can be included in RO membranes to reduce biofouling. However, the use of nanomembranes for commercial and industrial RO applications is still under development as their scalability is still a challenge. Polymeric membranes, such as cellulose acetate and polyamide, and their integration with other polymers or nanoparticles have also been presented in this paper. Overall, the choice of membrane materials for future RO processes would depend largely on the required permselectivity and the targeted foulants. However, membrane performance and antifouling features would have to be taken into consideration for sustainability of the type of RO membrane desired for a specific application.

Enhanced sludge properties and distribution study of sludge components in electrically-enhanced membrane bioreactor

This study investigated the impact of electric field on the physicochemical and biological characteristics of sludge wasted from an electrically-enhanced membrane bioreactor treating medium-strength raw wastewater. This method offers a chemical-free electrokinetic technique to enhance sludge properties and remove heavy metals. For example, sludge volume index (SVI), time-to-filter (TTF), mean sludge particle diameter (PSD), viscosity, and oxidation-reduction potential (ORP) of 21.7 mL/g, 7 min, 40.2 μm, 3.22 mPa s, and -4.9 mV were reported, respectively. Also, X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses provided mechanisms for heavy metal removal so as to establish relevant pathways for nutrient recovery. Furthermore, variations in dissolved oxygen (DO), conductivity, viscosity, ORP, total suspended solids (MLSS), and volatile suspended solids (MLVSS) were interrelated to evaluate the quality of wasted sludge. A pathway study on the transport and chemical distribution of nutrients and metals in sludge showed great potential for metal removal and nutrient recovery.

Leaching of PVP from PVDF/PVP blend membranes: impacts on membrane structure and fouling in membrane bioreactors

Polyvinylidene fluoride (PVDF) membranes are widely used in membrane industry, especially for membrane bioreactors (MBRs). Many PVDF membranes contain residual polyvinyl pyrrolidone (PVP) that acts as a pore-forming additive. The presence of residual PVP in some commercial PVDF membranes is often not specified and, therefore, its impact is mostly overlooked in the literature. In this study, we investigated the effect of PVP leaching on membrane structure and its implication on membrane fouling in a lab-scale MBR. PVP leaching can occur in two ways: (1) over the course of filtration from PVDF/PVP blend membranes or (2) prior filtration operation by treating the aforementioned membrane. We prepared PVDF, PVDF/PVP blend, and PVDF/PVP blend post-treated with sodium hypochlorite (NaClO), then assessed their performance. Leaching of PVP prior to the filtration operation significantly enlarged membrane pore size and thus reduced the membrane resistance. However, this advantage was dismissed during operation in MBR because PVP leaching also induced surface hydrophobicity that promoted membrane fouling, suggesting the detrimental effect of post-treatment. For PVDF/PVP blend sample, two counter-acting phenomena occurred: (1) slow leaching of PVP which gradually enlarged the membrane pores and rendered the membrane surface more hydrophobic and (2) adsorption of foulants that formed a secondary layer atop of membrane surface, restricted the pore mouth, and rendered the surface hydrophilic. The findings are significant since the change of membrane morphology over the course of filtration, as demonstrated in this study, is often overlooked when assessing membrane performance.

Molecular and ionic-scale chemical mechanisms behind the role of nitrocyl group in the electrochemical removal of heavy metals from sludge

The chemical basis for improved removal rates of toxic heavy metals such as Zn and Cu from wastewater secondary sludge has been demonstrated in this study. Instead of using excess corrosive chemicals as the source of free nitrous acid (FNA) for improved solubility of heavy metals in the sludge (in order to enhance electrokinetics), an optimized use of aqua regia has been proposed as an alternative. Fragments of nitrocyl group originated from aqua regia are responsible for the disruption of biogenic mixed liquor volatile suspended solids (MLVSS) and this disruption resulted in enhanced removal of exposed and oxidized metal ions. A diversity of nitric oxide (NO), peroxy nitrous acid, and peroxy nitroso group are expected to be introduced in the mixed liquor by the aqua regia for enhanced electrochemical treatment. The effects of pectin as a post treatment on the Zn removal from sludge were also presented for the first time. Results revealed 63.6% Cu and 93.7% Zn removal efficiencies, as compared to 49% Cu and 74% Zn removal efficiencies reported in a recent study. Also, 93.3% reduction of time-to-filter (TTF), and 95 mL/g of sludge volume index (SVI) were reported. The total operating cost obtained was USD 1.972/wet ton.

Comparative cradle-to-grave life cycle assessment of biogas production from marine algae and cattle manure biorefineries

The environmental impacts resulting from the cradle-to-grave life cycles of Enteromorpha prolifera macroalgae and cattle manure biorefineries are assessed and compared. Sensitivity analysis is carried out to evaluate the response of the impacts to changes in biogas application by using Simapro 7.3.3. Three scenarios are considered in the biorefineries. In the first and second scenarios, the biogas produced is considered to be used for electricity production and transportation, respectively. In the third scenario, the biogas is considered to be recycled back to the systems. Process energy requirements and transportation of inputs contribute the largest share of the overall impacts. The cattle manure biorefinery is slightly more eco-friendly than the macroalgae biorefinery in Scenarios 1 and 2 because it requires more eco-friendly inputs. However, the macroalgae biorefinery becomes more eco-friendly than the cattle manure biorefinery in Scenario 3 because macroalgae require less energy and water for biogas production.

Membrane bioreactors and electrochemical processes for treatment of wastewaters containing heavy metal ions, organics, micropollutants and dyes: Recent developments

Research and development activities on standalone systems of membrane bioreactors and electrochemical reactors for wastewater treatment have been intensified recently. However, several challenges are still being faced during the operation of these reactors. The current challenges associated with the operation of standalone MBR and electrochemical reactors include: membrane fouling in MBR, set-backs from operational errors and conditions, energy consumption in electrochemical systems, high cost requirement, and the need for simplified models. The advantage of this review is to present the most critical challenges and opportunities. These challenges have necessitated the design of MBR derivatives such as anaerobic MBR (AnMBR), osmotic MBR (OMBR), biofilm MBR (BF-MBR), membrane aerated biofilm reactor (MABR), and magnetically-enhanced systems. Likewise, electrochemical reactors with different configurations such as parallel, cylindrical, rotating impeller-electrode, packed bed, and moving particle configurations have emerged. One of the most effective approaches towards reducing energy consumption and membrane fouling rate is the integration of MBR with low-voltage electrochemical processes in an electrically-enhanced membrane bioreactor (eMBR). Meanwhile, research on eMBR modeling and sludge reuse is limited. Future trends should focus on novel/fresh concepts such as electrically-enhanced AnMBRs, electrically-enhanced OMBRs, and coupled systems with microbial fuel cells to further improve energy efficiency and effluent quality.

Polymers for Membrane Filtration in Water Purification

Polymers are sometimes preferred for membrane filtration because they are more flexible, easier to handle, and less expensive than inorganic membranes fabricated from oxides, metals, and ceramics. The polymers are used as the membrane active layer and porous support in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF) processes. However, the application of polymers for filtration suffers critical drawbacks, such as the chemical attack of polymers, membrane fouling, and hydrophobicity of most polymers. In this chapter, the polymers used for membrane filtration in recent studies and their fabrication procedures are presented and discussed. The polymers used in recent applications include cellulose acetate (CA), polyamide (PA), polyvinylidene fluoride (PVDF), polysulfone (PSF), polyethersulfone (PES), polyvinyl chloride (PVC), polyimide (PI), polyacrylonitrile (PAN), polyethylene glycol (PEG), polyvinyl alcohol (PVA), poly(methacrylic acid) (PMAA), poly(arylene ether ketone) (PAEK), poly(ether imide) (PEI), and polyaniline nanoparticles (PANI). A new polymeric material named polyethersulfone amide (PESA) has also been presented recently. Most of the recent studies have focused on improving the specific energy consumption, salt rejection, water flux, chemical resistance and antifouling properties of polymeric membranes and nanocomposites through blending and surface modification techniques. These techniques involve the use of zwitterionic coatings, sulfonated poly(arylene ether sulfone) (SPAES), perfluorophenyl azide (PFPA), carbon nanotubes (CNTs) and graphene oxide (GO) as nanofillers, polyether ether ketone (PEEK), and nanoparticles such as titanium dioxide (TiO2), and mesoporous silica. The use of polymers for filtration is still gaining tremendous attention, and further improvements of polymeric characteristics for enhanced membrane performance are expected in the coming years.

Multivariable statistical analysis for enhancing performance indicators in direct contact membrane distillation

Orthogonal experimental design, correlation analysis and response surface charts were used to identify the parameters influencing the operational efficiency of direct contact membrane distillation (DCMD). The orthogonal array design method was used to optimize the number of experimental trials required for dependence analysis. The operating factors studied were hot feed properties (temperature, salinity, flowrate) and cold distillate characteristics (temperature, and flowrate). The impact of those factors on three DCMD performance indicators - cold distillate production rate, performance ratio and recovery ratio – was investigated. The most significant factors influencing each performance indicator were obtained from the quantitative values of main and interaction effects, and confirmed by using the Pearson product-moment correlation coefficients. The main effects of feed and distillate temperatures on the performance indicators were the greatest, indicating that the most significant factors were the feed and distillate temperatures. The maximum distillate production rate was obtained at feed and distillate temperatures of 90 and 15°C, respectively. The optimum recovery and performance ratios were obtained at a feed flowrate of 1.6 L/min but when feed temperature was kept at 70°C.