Amos Bick

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.

Assessing the linkage between feed water quality and reverse osmosis membrane performance

The scarcity of fresh water in most of the countries in the Mediterranean Basin makes desalinated seawater a valuable alternative water source. It is therefore imperative to develop and adapt reverse osmosis (RO) methods to minimize water production expenses. Management modeling allows identifying preferable directions of implementation. Usually, desalination depends on a combination of a series of controlling parameters. These include feed water quality; required resulting qualities; and operational conditions determined by the membrane characteristics, flux and operating pressure head. Frequently it is difficult to select the best membrane for the RO process due to the complexity of the processes and the abundance of information that is provided by the membrane manufacturers. Taking available data (from RO membrane manufacturer catalogues) enables defining clusters of parameters with similar properties for improved control of the desalination process. According to the analysis, it was shown that there is a similar parameterization between the Silt Density Index (SDI) and the membrane flow rate. Other clusters were found as well. This analysis can be further developed into larger clusters leading to distinguishing two major facets: (1) the permeate and (2) RO membrane rejection; each includes several parameters. This showed that corresponding managing tools can simplify the membrane selection process and ultimately diminish production expenses.

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.

Analysis of membrane bioreactor performance for wastewater treatment using ranking methods

ABSTRACT The research compares four types of different designs of membrane bioreactors: (1) with 295-mm draft tube and without plastic carriers; (2) plastic carriers and 295-mm draft tube; (3) plastic carriers and 235-mm draft tube with two meshes around the bottom and top of a draft tube; and (4) plastic carriers without a draft tube. The feed for the reactors was artificial wastewater made from domestic wastewater and chicken manure, and membrane test data were based on a hollow fiber membrane module under ambient desert conditions. Process operation type D is the optimal choice. Mathematical analysis using total ranking methods, multi-indicator decision-making, and Hasse diagram support this choice. Concerning analysis by the different tools, inconsistencies between the rankings are noticed. Partial order ranking, as a method without any pre-assumptions concerning the possible relation between the single parameters, proves to be an elegant ranking method.