Irrigation with permeates to upgrade the quality of red pepper: a case study in Arava region, Israel.

Management of environmental resources presents challenges across agricultural production. In the case of the semi-arid region of Arava Valley in Israel, irrigation with groundwater brackish water is a widespread practice that has severe limitations. In this research studies are taking place for brackish groundwater upgrading for unrestricted use for the irrigation and sustainable agricultural production. The treatment system applies two main treatment stages: nanofiltration and reverse osmosis membrane process and, the pilot system with a capacity of around 1 m3/hr. Different mixtures of nanofiltration and reverse osmosis, Brackish and potable permeates are then applied for the irrigation of pepper crops. The field results with the graphical visualization approach using total ranking, multi-dimensional scaling, and clustering technique show that the conventional brackish feed water produces good results of relaxation time, total soluble solids and Vitamin C content. Treatment system using hybrid nanofiltration and reverse osmosis technology improves product quality related to the relative fruit colour red shade.

Relation between EPS adherence, viscoelastic properties, and MBR operation: Biofouling study with QCM-D.

Membrane fouling is one of the main constraints of the wide use of membrane bioreactor (MBR) technology. The biomass in MBR systems includes extracellular polymeric substances (EPS), metabolic products of active microbial secretion that adversely affect the membrane performance. Solids retention time (SRT) in the MBR is one of the most important parameters affecting membrane fouling in MBR systems, where fouling is minimized at optimal SRT. Among the operating parameters in MBR systems, SRT is known to strongly influence the ratio of proteins to polysaccharides in the EPS matrix. In this study, we have direct evidence for changes in EPS adherence and viscoelastic properties due to changes in the sludge removal rate that strongly correlate with the membrane fouling rate and EPS composition. EPS were extracted from a UF membrane in a hybrid growth MBR operated at sludge removal rates of 59, 35.4, 17.7, and 5.9 L day(-1) (corresponding SRT of 3, 5, 10, and 30 days, respectively). The EPS adherence and adsorption kinetics were carried out in a quartz crystal microbalance with dissipation monitoring (QCM-D) technology in several adsorption measurements to a gold sensor coated with Polyvinylidene Fluoride (PVDF). EPS adsorption to the sensor surface is characterized by a decrease of the oscillation frequency and an increase in the dissipation energy of the sensor during parallel flow of aqueous media, supplemented with EPS, above the sensor surface. The results from these experiments were further modeled using the Voigt based model, in which the thickness, shear modulus, and shear viscosity values of the adsorbed EPS layers on the PVDF crystal were calculated. The observations in the QCM-D suggested that the elevated fouling of the UF membrane is due to higher adherence of the EPS as well as reduction in viscosity and elasticity of the EPS adsorbed layer and elevation of the EPS fluidity. These results corroborate with confocal laser scanning microscopy (CLSM) image analysis showing thicker EPS in close proximity to the membrane surface operated at reactor conditions which induced more fouling at elevated sludge removal rates.

Pretreatment of wastewater: optimal coagulant selection using Partial Order Scaling Analysis (POSA).

Jar-test is a well-known tool for chemical selection for physical-chemical wastewater treatment. Jar test results show the treatment efficiency in terms of suspended matter and organic matter removal. However, in spite of having all these results, coagulant selection is not an easy task because one coagulant can remove efficiently the suspended solids but at the same time increase the conductivity. This makes the final selection of coagulants very dependent on the relative importance assigned to each measured parameter. In this paper, the use of Partial Order Scaling Analysis (POSA) and multi-criteria decision analysis is proposed to help the selection of the coagulant and its concentration in a sequencing batch reactor (SBR). Therefore, starting from the parameters fixed by the jar-test results, these techniques will allow to weight these parameters, according to the judgments of wastewater experts, and to establish priorities among coagulants. An evaluation of two commonly used coagulation/flocculation aids (Alum and Ferric Chloride) was conducted and based on jar tests and POSA model, Ferric Chloride (100 ppm) was the best choice. The results obtained show that POSA and multi-criteria techniques are useful tools to select the optimal chemicals for the physical-technical treatment.

Minimizing health risks during secondary effluent application via subsurface drip irrigation.

Health risks posed on consumers due to the use of agricultural products irrigated with reclaimed wastewater were assessed by numerical simulation. The analysis is based on defining of an Exposure Model (EM) which takes into account several parameters: (i) the quality of the applied wastewater, (ii) the irrigation method, (iii) the elapsed times between irrigation, harvest, and product consumption, and; (iv) the consumers' habits. The exposure model is used for numerical simulation of human consumers' risks by running the Monte Carlo simulation method. Although some deviations in the numerical simulation which are probably due to uncertainty (impreciseness in quality of input data) and variability due to diversity among populations reasonable results were accepted. Accordingly, there is a several orders of magnitude difference in the risk of infection between the different exposure scenarios with the same water quality. The variability indicates the need for setting risk-based criteria for wastewater reclamation, including the application method and environmental conditions, rather than single water quality guidelines. Extra data is required to decrease uncertainty in the risk assessment. Future research needs to include definite acceptable risk criteria, more accurate dose-response modeling, information regarding pathogen survival in treated wastewater, additional data related to the passage of pathogens into and in the plants during irrigation, and information referring to the consuming habits of the human community.

Extracellular polymeric substances (EPS) in a hybrid growth membrane bioreactor (HG-MBR): viscoelastic and adherence characteristics.

Extracellular polymeric substances (EPS) comprising the microbial biofilms in membrane bioreactor (MBR) systems are considered the most significant factor affecting sludge viscoelastic properties as well as membrane fouling. Understanding the water chemistry effects on EPS viscoelastic, conformational, and adherence properties are critical for defining the microbial biofilm's propensity of fouling the membrane surface. In this study, EPS extracted from a hybrid growth membrane bioreactor (HG-MBR) were analyzed for their adherence, viscoelastic properties and size distribution using quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS), respectively. Also, adsorption characteristics of EPS extracted from different locations in the HG-MBR (bioreactor liquor, fluidized carriers, and membrane surface) were defined and linked to the extent of the total polysaccharide content in the EPS. In accordance with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, more EPS were adsorbed at higher ionic strength, lower pH and in the presence of calcium cations. Based on the QCM-D results, the calculated thickness of the EPS adsorbed layer was increased at lower ionic strength, higher pH, and only had a minor increase in the presence of calcium cations. The calculated shear modules and shear viscosity suggest that at lower pH and in the presence of calcium, EPS becomes more viscous and elastic, respectively. DLS analysis correlated to the QCM-D results: A decrease in the hydrodynamic radius of the EPS colloids was observed at lower pH, and in the presence of calcium, most likely attributed to intermolecular attraction forces. Based on this study, low pH and presence of calcium may induce flocs' stability that resist erosion in the MBRs, while on the other hand, these conditions may induce the formation of an elastic and viscous EPS layer fouling the ultrafiltration (UF) membrane.

Membrane technology for sustainable treated wastewater reuse: agricultural, environmental and hydrological considerations.

Field experiments were conducted in agricultural fields in which secondary wastewater of the City of Arad (Israel) is reused for irrigation. For sustainable agricultural production and safe groundwater recharge the secondary effluent is further polished by a combined two-stage membrane pilot system. The pilot membrane system consists of two main in row stages: Ultrafiltration (UF) and Reverse Osmosis (RO). The UF stage is efficient in the removal of the pathogens and suspended organic matter while the successive RO stage provides safe removal of the dissolved solids (salinity). Effluents of various qualities were applied for agricultural irrigation along with continuous monitoring of the membrane system performance. Best agricultural yields were obtained when applying effluent having minimal content of dissolved solids (after the RO stage) as compared with secondary effluent without any further treatment and extended storage. In regions with shallow groundwater reduced soil salinity in the upper productive layers, maintained by extra membrane treatment, will guarantee minimal dissolved solids migration to the aquifers and minimize salinisation processes.

Secondary wastewater polishing with ultrafiltration membranes for unrestricted reuse: fouling and flushing modeling.

The effects of operating parameters such astransmembrane pressure, retentate, and recirculation volumetric flow rates on the productivity of an ultrafiltration membrane were studied using field data and development of a management model. Correlation equations for predicting the volumetric permeate flow rates were derived from general membrane blocking laws and experimental data. The experimental data were obtained from a pilot study carried out in the Arad wastewater treatment system (a pilot plant operating in feed and bleed operation mode) located several kilometers west of the City of Arad, Israel. Correlation predictions were confirmed with the independent experimental results. The results enabled us to develop a mathematical expression accurately describing the decline in flux due to fouling.