On day 49, excessive foaming was observed in the upper part of the anaerobic reactor. LAS analysis revealed a concentration of 5.9 mg LAS·L−1in the wastewater (lot 7), around six times greater than the values of the previous lots (always lower than 1 mg.L−1).
Changes in the wastewater constituents may cause a disturbance in the anaerobic reactor and, consequently, in the entire system. Analyzed methanogenesis inhibition caused by different levels of LAS present in domestic wastewater and found a reduction of 30% in methanogenesis activity when the LAS concentration was increased from 0 to 10 mg LAS·L−1, and 50% when the surfactant concentration was 30 mg LAS·L−1.
In our study, the anaerobic biomass had never faced a LAS concentration higher than 1 mg LAS·L−1; thus, a small increase in the surfactant content caused the observed disturbance. During the use of lot 7, between days 49 and 59, considering the anaerobic reactor, ORP reached −162.3 mV, the alkalinity was consumed, pH dropped to the lowest value of 6.4, and COD, sulphate, and colour removal efficiencies decreased to 30, 53 and 0%, respectively.
A potentiometric titration method was applied to the determination of surface charge density of the examined systems and their points of zero charge (pzc). The pzc is at such pH value at which the concentration of positively and negatively charged surface groups is the same and thus σ0 = 0. Dependencies of σ0 as a function of solution pH (changing in the range 3-11) were calculated by the special software “titr_v3”. The examined solution (of volume 50 mL) was introduced to the Teflon vessel thermostated (20 °C) using thermostat RE 204 (Lauda, Germany). The glass and calomel electrodes (Beckman Instruments) as well as pH-meter PHM 240 (Radiometer, Sweden) were used to continuous control of system’s pH during titration, which was performed by the use of automatic microburette Dosimat 765 (Metrohm, Switzerland) and computer. The examined systems were titrated with NaOH solution of concentration 0.1 mol/L and the applied solid mass was 0.1 g.
Classical salt coagulants have some drawbacks as the efficiency of the coagulation flocculation process strongly depends on pH. The chemical speciation of the coagulant, the surface charge of colloid and sometimes the charge of soluble molecule depend on pH. Moreover, the process is not always efficient enough because at different environmental conditions such as at extreme pH and at very low or very high temperature, it may produce very sensitive and fragile flocs, which result in poor sedimentation. These flocs may rupture under any type of physical forces. To select the coagulation pH, wastewaters adjusted to desirable pH values were introduced in a serial of 1000 ml work volume beakers. Then a known volume of prepared TBP solution was added to each jar and placed in jar test apparatus. The effect of coagulation pH on COD removal from jar tests for coagulation of textile, paint and tannery wastewaters is shown in Figure 2. It can be seen that Initial pH did not clearly affect TBP effect on COD removal from industrial wastewaters. At pH values ranged from 4 to 12, COD removal were 48–51% from textile wastewater and 58–61% from paint and tannery wastewaters. Therefore, the process implicating TBP does not require coagulation pH adjustment. This non dependence on pH is an advantage in the coagulation–flocculation process.
The objective of the present study was to study the environmental impact associated with the treatment of industrial textile effluent. The two possible scenarios considered in the present study included a conventional treatment system and a ZLD treatment system. Carbon footprint was used as the parameter to comparatively analyze the environmental impact of considered scenarios. Carbon footprint calculation methodology was developed for the application to the wastewater treatment sector in developing countries. Actual field-scale data were collected through extensive industrial visits for the carbon footprint analysis. The expected research outcome included significant inputs for the decision-making authorities towards the establishment of either the conventional or ZLD effluent treatment system.
The following section on methods and techniques includes the details of the proposed carbon footprint calculation methodology. Various steps of carbon footprint analysis applied to conventional and ZLD treatment systems are presented in this section. It is followed by the results and discussion on the finding of comparative carbon footprint analysis. Lastly, the conclusion section presents the collective findings of present research along with the key inputs to textile manufacturers on the selection of appropriate textile effluent treatment system.