George M. Ayoub

High-pH-magnesium coagulation-flocculation in wastewater treatment

Abstract Chemically enhanced wastewater treatment is attracting substantial interest, especially for wastewaters that are not amenable to treatment by conventional biological treatment strategies. Among the currently employed chemical unit processes in wastewater treatment, coagulation–flocculation has received considerable attention for yielding high pollutant removal efficiency. Over the past years, several authors have investigated the role of magnesium ions as a potential coagulant for the chemical clarification of wastewater. This paper presents a comprehensive review of high-pH–magnesium coagulation–flocculation processes in wastewater treatment, describes their applicability and reveals the contribution of such treatment strategies to the chemical clarification of various wastewaters. More importantly, the paper discusses the advantages, disadvantages and process efficiency of high-pH–magnesium coagulation–flocculation in relation to various sources of magnesium ions. The characteristics of sludges produced from lime-based chemical wastewater treatment processes are also discussed. Finally, factors impacting the economics of the process are considered to estimate the costs incurred.

Do biological-based strategies hold promise to biofouling control in MBRs?

Biofouling in membrane bioreactors (MBRs) remains a primary challenge for their wider application, despite the growing acceptance of MBRs worldwide. Research studies on membrane fouling are extensive in the literature, with more than 200 publications on MBR fouling in the last 3 years; yet, improvements in practice on biofouling control and management have been remarkably slow. Commonly applied cleaning methods are only partially effective and membrane replacement often becomes frequent. The reason for the slow advancement in successful control of biofouling is largely attributed to the complex interactions of involved biological compounds and the lack of representative-for-practice experimental approaches to evaluate potential effective control strategies. Biofouling is driven by microorganisms and their associated extra-cellular polymeric substances (EPS) and microbial products. Microorganisms and their products convene together to form matrices that are commonly treated as a black box in conventional control approaches. Biological-based antifouling strategies seem to be a promising constituent of an effective integrated control approach since they target the essence of biofouling problems. However, biological-based strategies are in their developmental phase and several questions should be addressed to set a roadmap for translating existing and new information into sustainable and effective control techniques. This paper investigates membrane biofouling in MBRs from the microbiological perspective to evaluate the potential of biological-based strategies in offering viable control alternatives. Limitations of available control methods highlight the importance of an integrated anti-fouling approach including biological strategies. Successful development of these strategies requires detailed characterization of microorganisms and EPS through the proper selection of analytical tools and assembly of results. Existing microbiological/EPS studies reveal a number of implications as well as knowledge gaps, warranting future targeted research. Systematic and representative microbiological studies, complementary utilization of molecular and biofilm characterization tools, standardized experimental methods and validation of successful biological-based antifouling strategies for MBR applications are needed. Specifically, in addition, linking these studies to relevant operational conditions in MBRs is an essential step to ultimately develop a better understanding and more effective and directed control strategy for biofouling.

Seawater induced algal flocculation

Abstract The effectiveness of the use of seawater in the removal of algae from oxidation pond effluents was investigated. Freshly collected samples of pond effluent were initially adjusted to pH levels of 9.0–11.5, then seawater in proportions of 0–20% (v/v) was added. The jar test technique was used to determine algal removal efficiencies. The effect of the process on alkalinity in the samples was studied. Test results indicated that the primary reactions responsible for the removal of algae were the formation and precipitation of CaCO3 and Mg(OH)2. These reactions were initiated at pH values of 9.5 and 11.0, respectively, in the absence of seawater. As seawater concentrations were increased, the reactions were initiated at lower pH values. Algal removals in excess of 80% were achieved at an initial pH of 10.5 and 5–10% seawater. Nearly complete removal (> 95%) was achieved at an initial pH of 11.0 and 10–15% seawater.

An optimisation model for regional integrated solid waste management I. Model formulation.

Increased environmental concerns and the emphasis on material and energy recovery are gradually changing the orientation of MSW management and planning. In this context, the application of optimisation techniques have been introduced to design the least cost solid waste management systems, considering the variety of management processes. This study presents a model that was developed and applied to serve as a solid waste decision support system for MSW management taking into account both socio-economic and environmental considerations. The model accounts for solid waste generation rates, composition, collection, treatment, disposal as well as potential environmental impacts of various MSW management techniques. The model follows a linear programming formulation with the framework of dynamic optimisation. The model can serve as a tool to evaluate various MSW management alternatives and obtain the optimal combination of technologies for the handling, treatment and disposal of MSW in an economic and environmentally sustainable way. The sensitivity of various waste management policies will be also addressed. The work is presented in a series of two papers: (I) model formulation, and (II) model application and sensitivity analysis.

Developments in Solar Still Desalination Systems: A Critical Review

Solar still desalination uses a sustainable and pollution-free source to produce high-quality water. The main limitation is low productivity and this has been the focus of intensive research. A major concern while increasing productivity is to maintain economic feasibility and simplicity. The authors present a critical review of the research work conducted on solar stills development. Studies addressing each parameter of concern are grouped together and results compared. Novelty in design and newly introduced features are presented. Modeling efforts of flow circulation within the still and methods to estimate internal heat transfer coefficients are discussed and future research needs are outlined.

Impact of intermittent water supply on water quality in Lebanon

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An optimisation model for regional integrated solid waste management II. Model application and sensitivity analyses

Increased environmental concerns and the emphasis on material and energy recovery are gradually changing the orientation of MSW management and planning. In this context, the application of optimisation techniques have been introduced to design the least cost solid waste management systems, considering the variety of management processes (recycling, composting, anaerobic digestion, incineration, and landfilling), and the existence of uncertainties associated with the number of system components and their interrelations. This study presents a model that was developed and applied to serve as a solid waste decision support system for MSW management taking into account both socio-economic and environmental considerations. The model accounts for solid waste generation rates, composition, collection, treatment, disposal as well as potential environmental impacts of various MSW management techniques. The model follows a linear programming formulation with the framework of dynamic optimisation. The model can serve as a tool to evaluate various MSW management alternatives and obtain the optimal combination of technologies for the handling, treatment and disposal of MSW in an economic and environmentally sustainable way. The sensitivity of various waste management policies is also addressed. The work is presented in a series of two papers: (I) model formulation, and (II) model application and sensitivity analysis.

Temporal variation of leachate quality in seawater saturated fills

Many waste fills are located along the coast, often encroaching into the sea, and are consequently subjected to seawater intrusion. Although previous investigations have demonstrated the beneficial effects of moisture addition on biodegradation processes, these studies have not considered the potential effects of seawater intrusion into a sea fill. In this study, a preliminary laboratory-scale experiment was conducted to evaluate the potential effects of seawater intrusion on biodegradation processes and leachate quality. Chemical analysis was performed on leachate samples for a period of 230 days to study the temporal variation of leachate quality in the early stages of refuse decomposition. Leachate samples were collected weekly and several parameters were monitored including pH, COD, TOC, TDS, EC, chlorides, sulfates, orthophosphates, nitrates, ammoniacal nitrogen, hardness, and heavy metals. Chemical concentration levels were related to biological activity within the test cells, and the results indicate that salt water could delay MSW biodegradation.

Seawater flocculation of emulsified oil and alkaline wastewaters

Abstract Seawater flocculation at high pH was investigated for the removal of emulsified oil and suspended solids from wastewater. As little as 2% seawater by volume, in conjunction with lime or caustic for pH adjustment, was required to achieve good flocculation of the oil-water emulsion. The same amount of seawater allowed efficient removal of suspended solids from alkaline industrial wastewaters and oxidation pond effluent having pH of 10.6 and higher, without addition of an OH − source. Effective flocculation was associated with the precipitation of 2–3.5 g equiv m −3 of Mg 2+ . The minimum seawater concentration for effective flocculation, in relation to pH, was predicted successfully based on the solubility of magnesium in wastewater-seawater mixtures.

THE SOLID WASTE MANAGEMENT SCENE IN GREATER BEIRUT

The magnitude of the solid waste problem in Beirut (Lebanon) is apparent to any onlooker. Waste collection has improved recently but is frequently incomplete and sometimes sporadic. Considerable labour problems exist and are made worse by the disruption from the aftermath of civil war. The most suitable future disposal methods have not been fully studied, and existing disposal sites and plants are near to saturation or collapse. In order to start a new waste management study correctly, the first step was to analyse the waste composition, characteristics and generation rates. The authors attempt to show that some form of incineration with energy recovery may be the preferred disposal option given the current local prevailing social conditions. Composting is argued to be the next choice. Direct landfill of untreated waste is the choice for the present time, but its continuance is open to question if new landfills are not identified and permitted to be used.