Lucy Semerjian

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.

Equilibrium and kinetics of cadmium adsorption from aqueous solutions using untreated Pinus halepensis sawdust

Untreated Pinus halepensis sawdust has been investigated as an adsorbent for the removal of cadmium from aqueous solutions. Batch experiments were carried out to investigate the effect of pH, adsorbent dose, contact time, and metal concentration on sorption efficiency. The favorable pH for maximum cadmium adsorption was at 9.0. For the investigated cadmium concentrations (1-50mg/L), maximum adsorption rates were achieved almost in the 10-20 min of contact. An adsorbent dose of 10 g/L was optimum for almost complete cadmium removal within 30 min from a 5mg/L cadmium solution. For all contact times, an increase in cadmium concentration resulted in decrease in the percent cadmium removal (100-87%), and an increase in adsorption capacity (0.11-5.36 mg/g). The equilibrium adsorption data were best fitted with the Freundlich isotherm (R(2)=0.960). The kinetics of cadmium adsorption was very well described by the pseudo-second-order kinetic model (R(2)>0.999).

Reactor performance in terms of COD and nitrogen removal and bacterial community structure of a three-stage rotating bioelectrochemical contactor.

Integrating microbial fuel cell (MFC) into rotating biological contactor (RBC) creates an opportunity for enhanced removal of COD and nitrogen coupled with energy generation from wastewater. In this study, a three-stage rotating bioelectrochemical contactor (referred to as RBC-MFC unit) integrating MFC with RBC technology was constructed for simultaneous removal of carbonaceous and nitrogenous compounds and electricity generation from a synthetic medium containing acetate and ammonium. The performance of the RBC-MFC unit was compared to a control reactor (referred to as RBC unit) that was operated under the same conditions but without current generation (i.e. open-circuit mode). The effect of hydraulic loading rate (HLR) and COD/N ratio on the performance of the two units was investigated. At low (3.05 gCOD g⁻¹N) and high COD/N ratio (6.64 gCOD g⁻¹N), both units achieved almost similar COD and ammonia-nitrogen removal. However, the RBC-MFC unit achieved significantly higher denitrification and nitrogen removal compared to the RBC unit indicating improved denitrification at the cathode due to current flow. The average voltage under 1000 Ω external resistance ranged between 0.03 and 0.30 V and between 0.02 and 0.21 V for stages 1 and 2 of the RBC-MFC unit. Pyrosequencing analysis of bacterial 16S rRNA gene revealed high bacterial diversity at the anode and cathode of both units. Genera that play a role in nitrification (Nitrospira; Nitrosomonas), denitrification (Comamonas; Thauera) and electricity generation (Geobacter) were identified at the electrodes. Geobacter was only detected on the anode of the RBC-MFC unit. Nitrifiers and denitrifiers were more abundant in the RBC-MFC unit compared to the RBC unit and were largely present on the cathode of both units suggesting that most of the nitrogen removal occurred at the cathode.

A health‐based socio‐economic assessment of drinking water quality: the case of Lebanon

Water‐related diseases are a human tragedy, resulting in millions of deaths each year, preventing millions more from leading healthy lives, and undermining development efforts by burdening the society with substantial socio‐economic costs. This problem is of great significance in developing countries, where polluted water, water shortages, and unsanitary living conditions prevail. This paper presents a case study on a health‐based socio‐economic assessment of drinking water quality in Lebanon, based on relevant valuation approaches and available country‐specific data. The assessment revealed that the potential health and economic benefits due to water and sanitation improvements can be significant (0.15‐3.35 percent of GDP).

Assessment of the performance of SMFCs in the bioremediation of PAHs in contaminated marine sediments under different redox conditions and analysis of the associated microbial communities.

The biodegradation of naphthalene, 2-methylnaphthalene and phenanthrene was evaluated in marine sediment microbial fuel cells (SMFCs) under different biodegradation conditions, including sulfate reduction as a major biodegradation pathway, employment of anode as terminal electron acceptor (TEA) under inhibited sulfate reducing bacteria activity, and combined sulfate and anode usage as electron acceptors. A significant removal of naphthalene and 2-methylnaphthalene was observed at early stages of incubation in all treatments and was attributed to their high volatility. In the case of phenanthrene, a significant removal (93.83±1.68%) was measured in the closed circuit SMFCs with the anode acting as the main TEA and under combined anode and sulfate reduction conditions (88.51±1.3%). A much lower removal (40.37±3.24%) was achieved in the open circuit SMFCs operating with sulfate reduction as a major biodegradation pathway. Analysis of the anodic bacterial community using 16S rRNA gene pyrosequencing revealed the enrichment of genera with potential exoelectrogenic capability, namely Geoalkalibacter and Desulfuromonas, on the anode of the closed circuit SMFCs under inhibited SRB activity, while they were not detected on the anode of open circuit SMFCs. These results demonstrate the role of the anode in enhancing PAHs biodegradation in contaminated marine sediments and suggest a higher system efficiency in the absence of competition between microbial redox processes (under SRB inhibition), namely due to the anode enrichment with exoelectrogenic bacteria, which is a more energetically favorable mechanism for PAHs oxidation than sulfate.

Modeling the formation of trihalomethanes in drinking waters of Lebanon

The current research aims at developing predictive models for trihalomethane (THM) formation in Lebanon based on field-scale investigations as well as laboratory controlled experimentations. Statistical analysis on field data revealed significant correlations for TTHM with chlorine dose, Specific UV-A, and UV254 absorbing organics. Simulated distribution system-THM tests showed significant correlations with applied chlorine dose, total organic carbon, bromides, contact time, and temperature. Predictive models, formulated using multiple regression approaches, exhibiting the highest coefficients of determination were quadratic for the directly after chlorination (DAC; r2 = 0.39, p < 0.036) and network (r2 = 0.33, p < 0.064) THM databases, and logarithmic for the laboratory simulated THM database (r2 = 0.70, p < 0.001). Computed r2 values implied low correlations for the DAC and network THM database, and high correlation for the laboratory simulated THM database. Significance of the models were at the 0.05 level for DAC database, 0.10 level for the network database, and very high (<0.01 level) for the laboratory simulated THM database. It is noteworthy to mention that no previous attempts to assess, monitor, and predict THM concentrations in public drinking water have been reported for the country although a large fraction of the population consumes chlorinated public drinking water.

Physicochemical Evaluation of the Upper Litani River Watershed, Lebanon

This study aims to determine the extent of groundwater damage in the Upper Litani River Basin (ULRB) after years of water mismanagement and overfertilization in what is considered to be Lebanons largest fertile area. Physical and chemical samples were collected between 2005 and 2010 and analyzed using “The Standard Methods for the Examination of Water and Wastewater” (APHA, AWWA) in order to determine the extent of this pollution. The parameters included pH, ammonia, nitrate, nitrite, sulfate, phosphate, dissolved oxygen, and total dissolved solids.

Human health risk assessment of pharmaceuticals in treated wastewater reused for non-potable applications in Sharjah, United Arab Emirates

Pharmaceuticals and personal care products are an integral part of societal health yet their presence in various environmental compartments, including treated wastewaters, has sparked concerns towards possible human and ecological health effects. The current study aims to characterize human health risks posed by ten pharmaceuticals quantified in wastewater treatment plant effluents where water is reused mainly for landscape irrigation. Receptors were identified as children playing in green areas, adult landscape workers, and adult users of athletic and golf courses irrigated by treated wastewater. The human health risk assessment model exhibited safe exposure (RQ < 1) to all pharmaceuticals for all receptors through both dermal and ingestion exposure pathways. RQs were highest for the landscape worker followed by children playing in green areas and then adult using the athletic fields. RQs were highest to lowest in the following order of pharmaceuticals: acetaminophen, metoprolol, ciprofloxacin, erythromycin, ofloxacin, sulfadiazine, sulfamethoxazole, sulfapyridine, risperidone, and sulfamethazine. Such risk assessment findings aid in supporting decisions to optimize wastewater treatment and reuse strategies, as well as safeguard public and environmental health.

Low cost processes for the removal of phosphates in water and wastewater

This paper presents a synopsis of various low-cost techniques employed for the removal of phosphates from water and treated wastewater. Techniques employed include seawater flocculation and coagulation/flocculation using bittern, adsorption on fluidised raw dolomite bed, and filtration through iron and aluminium coated filter media. Seawater flocculation at a seawater concentration of 10% exhibited highly efficient (>90%) removal of Total Phosphorus (TP) from alkaline oxidation pond effluents. For experiments employing fluidised raw dolomite bed, varying degrees of phosphate adsorption capacities were observed for the different test influents used. Finally, laboratory experiments conducted to determine the efficacy of iron and aluminium coated media in removing low concentrations of phosphates indicated very effective phosphate removals (>90%) when applied to Distilled Water (DW) and synthetic groundwater, and less success when applied to Tap Water (TW) (<80%) and treated wastewater effluents (<70%).