Treatment of rubber wastewater using zinc sulphate as coagulants-data collection on removal efficiency for physicochemical and heavy metal parameters

This article provides data regarding the performance of zinc sulphate as a coagulant for treating rubber industry wastewater. The effect of four factors on removal efficiency of nine parameters is investigated, namely: pH, mixing speed, dosage of coagulant (zinc sulphate) and retention time. Response surface methodology was used to investigate the effect of selected variables. The data obtained from face centered composite design (FCCD) were analyzed by using analysis of variance (ANOVA) and regression model to find the optimum operating conditions for the selected factors.


Value of the Data
• The data produced an efficient method for rubber wastewater treatment using zinc sulphate as a coagulant. • The data has benefits for rubber industries to manage their wastewater effluents. Also the data provides significant knowledge and applications to the university postgraduate students and research centres.
• The data provides model that can be used for treatment of several types of industrial wastewater treatment.

Data Description
The raw data for thirty experiments using face centered composite design (FCCD), [2] covering all possible combinations of the selected variables (Dosage of zinc sulphate (A), pH (B), retention time (C) and mixing speed (D)) regarding measuring physiochemical parameters such as chemical oxygen demand (COD), total suspended solid (TSS), ammoniacal nitrogen (NH 3 -N), color and heavy metals (Pb, Fe, Zn, Cu, K) for rubber wastewater are presented in Table 1 . The results of the experiments were analyzed using analysis of variance (ANOVA) [3] . The independent variables (factors) and corresponding levels used for optimization of rubber wastewater treatment is summarized in Table 2 Table 3 and 4 (analysis of variance (ANOVA)). Mathematical models that show the effect of significant variables on selected parameters are presented in Table 5 and 6 respectively. The equations of coded factors for TSS, COD, Color, ammonia and heavy metals removal were presented in Tables 5 and 6 , respectively.

Sampling
20 l sample of rubber wastewater was collected from Tan Sin Lian Industries Sdn. Bhd, one of the gloves manufacturing companies that located in Kawasan Perindustrian Melekek, Alor Gajah, Malaysia. This company is a global glove manufacturing that operates for the past ten years. The sample was collected directly from production factory during the period between April and June 2019. Then, the sample was stored in the sealed plastics bottles and preserved at a temperature less than 4 °C before being used and analyzed. Then the sample was characterized following standard methods for water and wastewater analysis [4] .

Preparation of reagent
In this section rubber wastewater was coagulated using Zinc sulphate (ZnSO 4 ). A set of ZnSO 4 dosages were added to rubber wastewater samples gradually to determine the optimum conditions. The performance of the best dosage was selected based on COD, Color and NH 3 -N removal efficiencies. Orbital Shaker (Luckham R100/TW Rotatable Shaker 340 mm X 245 mm) with at 200 rpm was used for samples shaking [5] . All experiments were performed at room tempera- ture (28 °C) using 100 mL of rubber wastewater samples placed in conical flasks with a 250 mL capacity. pH of the samples was controlled by using 3 M of sulphuric acid solution and sodium hydroxide solution, respectively [6] . All experiments were performed at laboratory of Malaysian Institute of chemical & Bioengineering Technology, University of Kuala Lumpur, Melaka, Malaysia.  Table 2 .

Experimental design
The relationship between the selected factors ( A , B, C, D ) and each of the responses is usually described in response surface methodology (RSM) by a second-order polynomial as given in Eq. (1) .

Table 6
Equations of coded factors for heavy metals removal.

Analytical methods
COD, color and NH 3 -N, were immediately tested before and after each experiment using UV-VIS spectrophotometer (HACH DR 2800). Leachate sample was shacked well analyzed. NH 3 -N concentration was measured by the Phenol Method No. (4500) using a UV-VIS spectrophotometer at 640 nm with a light path of 1 cm or greater. pH was measured using a portable digital pH/Mv meter (Inolab pH 720, WTW 82362 Weilheim, Germany). COD concentration was determined by the open reflux method No. (5220). Heavy metals were tested by Atomic Absorption Spectroscopy (UNICAM 929 AA spectrometer). The test values are presented as the average of the three measurements, and the difference between the measurements of each value was less than 3%. The removal efficiencies of COD and NH3-N were obtained using the following Eq.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article.