Researches

Introduction In the future, the world is confronted with energy and freshwater shortage. Desalination of brackish or seawater is one of the most important ways to solve the water scarcity issue [1, 2]. The use of solar energy or waste heat sources is acceptable for water-producing systems of such a small size [3–5]. The relevancy of nanomaterials is to realize the best attainable properties within the smallest possible loadings through homogenized distribution and stable suspension of these nanoparticles[6–11]. Often, heat transfer improvement in solar collectors is one of the basic problems in energy saving, compact designs, and different operating temperatures. Researchers also investigated the multiwalled carbon nanotubes (MWCNTs) and water nanofluids with a pH of 3.5, 6.5, and 9.5, and Triton X-100 as a surfactant (0.2 wt %) using flat-plate solar collectors. It was found that the nanofluids have better heat transfer performance in acidic and alkaline water due to the influence of the isoelectric point. The higher efficiency (67 %) was obtained at pH 9.5 and 3.5 with a water flow rate of 0.0333 kg s–1. A stable nanofluid based on ethylene glycol-containing nanosheets of graphene oxide was prepared by Yu et al. [12]. The improvement in thermal conductivity relies strongly on the volume fraction of the nanosheet of graphene oxide and increases with higher nanoparticle loading. The heat efficiency was enhanced up to 61.0 % using a nanosheet loading of 5.0 vol %. For seven days, the thermal conductivity of the fluids remained almost constant, which suggests their high stability. In the measured temperature range, the enhancement value was independent of the temperature. Peyghambarzadeh et al. [13, 14] studied force convection techniques in an excessively base water nanofluid, which was experimentally compared to water in a vehicle heat exchanger with different nanofluid loadings. It was experimentally investigated to improve the rate of heat transfer. The variable effect of the inlet temperature of the fluid in the heat exchanger on the heat transfer coefficient was evaluated. The findings showed that the incremental fluid circulation rate would increase the output rate of heat transfer, while the temperature of the fluid entering the heat exchanger had negligible effects. Meanwhile, water nanofluid subservience at low-volume loadings would increase the heat transfer rate efficiency by approximately 44 % compared to water

 Introduction Industrial wastewater treatment, such as those used for tannery wastewater, is complex due to the variety of chemicals added at different stages of processing of hides and skins. Major problems in tanneries are due to wastewater containing heavy metals, toxic chemicals, chloride, lime with high dissolved and suspended salts and other pollutants (Uberoi, 2003). The tanning process and the effluents generated have already been reported in literature (Wiegant et al., 1999, Sreeram and Ramasami, 2003, Stoop, 2003). Many conventional processes were carried out to treat wastewater such as biological process (Ahn et al., 1996, Vijayaraghavan and Murthy, 1997, Wiemann et al., 1998, Di Iaconi et al., 2003, Farabegoli et al., 2004), oxidation process (Sekaran et al., 1996, Dogruel et al., 2004, Sacco et al., 2012, de Caprariis et al., 2012) and chemical process (Di Iaconi et al., 2001, Orhon et al., 1998, Song et al., 2004) etc. Among these, physical and chemical methods are considered very expensive in terms of energy and reagents consumption (Churchley, 1994, Stern et al., 2003), and generation of excessive sludge (Chu, 2001). To reduce the production of sludge by the treatment of this wastewater combined or alternative systems must be explored. In particular, in this work, two spiral wound membrane modules were used: nanofiltration (NF) and reverse osmosis (RO). The goal of this approach is to insert membranes into the cycle of wastewater treatment in order to remove the entire chain of biological treatment and the resulting post physico[1]chemical residue with a significant reduction of sludge up to 95%. A modified version of the traditional method used to measure critical fluxes of membranes, that is the pressure cycling method, was applied to measure both the critical and the threshold flux on the nanofiltration membrane in order to optimize the operating conditions. Once obtained the critical and threshold flux values, this data was used as input for a batch membrane process optimization method developed previously by Stoller at al. (Stoller and Chianese, 2006, Stoller and Bravi, 2010, Stoller, 2009, Iaquinta et al., 2009, Stoller, 2008, Stoller, 2011). The output of the method indicates the optimal permeate feed flow rate which should be used during the batch in order to inhibit membrane fouling. Finally, the obtained results were compared from an economical point of view with a conventional biological process to validate the membrane plant as possible alternative to conventional process.

ABSTRACT This study aims to establish an empirical correlation between biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) of the sewage flowing in Al-Diwaniyah wastewater treatment plant. The strength of the wastewater entering the plant varied from medium to high. High concentrations of BOD5 and COD in the effluent were obtained due to the poor performance of the plant. This was observed from the BOD5 /COD ratios that did not confirm with the typical ratios for the treated sewage. To improve the performance of this plant, regression equations for BOD5 and COD removal percentages were suggested which can be used to facilitate rapid effluent assessment or optimal process control. The equations relating the percentage removal of BOD5(y) with influent BOD5(x), y= 0.044x + 80.66 and the percentage removal of COD (y) with influent COD (x), y= 0.045x + 55.15 were found with high correlation R2 =0.72 and 0.86 respectively. Key words: Sewage treatment, BOD5, COD, BOD5/COD ratio, BOD5&COD correlations