Investigating the effect of operational parameters of a semi-industrial hydro-cyclone on the efficiency of Granite and Marble stones wastewater treatment

Introduction
The use of modern methods of recycling effluent with high treatment efficiency in compare to the traditional methods (the use of sedimentation ponds) is of great importance. One of the modern methods of treating these effluents is the use of filtering presses. A newer method is using hydro cyclones as a result of centrifugal hydrodynamic forces for separating solid particles from the effluent, e.g., stone powder in the current research, (Naderi et al.2019). In this regards, many researches have been done in the field of separation of two different phases of fluid using hydro cyclone in different hydraulic conditions and geometric parameters.

Materials and methods
Materials used in research
The materials used in this research were solid particles in the wastewater of the stone cutting factory of Mahmoudabad industrial town of Isfahan. The resulting slurry was collected in the factory and after drying and separation was used for the experiments. In this study, Granite and Marble stone powder with a density of 2750 and 3020 kgm-3 and a particle diameter distribution less than 600µm was used. Also, the effect of hydraulic parameters such as flow division ratio (under flow discharge to inlet flow discharge), wastewater weight concentration and inlet pressure on hydro cyclone performance with a cyclone diameter of 140 mm in the separation of Granite and Marble powder stone from wastewater was investigated.

Design of experiments
Experiments were designed by Design Expert.10 software with response level method (RSM). In conducting experiments, first, a solution of Granite and Marble powder stone with the desired concentrations (0.64 to 7.36% by weight) in a volume of 20 liters was prepared in a tank, and then this solution was circulated to the hydro cyclone by pressure with a centrifugal pump.
In each experiment, inlet perssure and overflow pressure were recorded using pressure guages and the volumetric flow rate from overflow and underflow was measured. Samples of overflow and underflow were taken with a specified volume and then stored and dried in an oven at 105ºC for 24 hours. The residual dry mattter mass was measured from the overflow and underflow samples, and the solid particle separation efficiency was computed from Eq. (1):
E=M_u/M×100 (1)
In this Equation, Mu is mass per unit volume of Granite and Marble stone powder inside the underflow (grl-1); M is total mass per unit volume of examined Granite and Marble stone powder in hydro cyclone inlet (total overflow and underflow; grl-1) and E is the efficiency of separation of solid particles from the feed.
Results and discussion
Influence of operating parameters of weight concentration of the feed (Cw), inlet pressure of the hydro cyclone (Pi), and the Ratio of outlet flow) under flow) from the discharge to inlet flow to the hydro cyclone (Rf) on the efficiency of the examined hydro cyclone is given in the form of Eq. (2) for Granite powder stone and Eq. (3) for Marble powder stone.

(2) Efficiency=93.16-1.01R_f-4.36C_w+10.01P_i+0.04R_f C_w-0.04R_f P_i+0.96 C_w P_i+8.12E-003*〖R^2〗_f -0.08*〖C^2〗_w-2.41* P_i ²


(3) Efficiency=116.26-2.11R_f-9.13C_w+6.22 P_i+0.11R_f C_w+0.17R_f P_i+1.22 C_w P_i+5.54E-003*〖R^2〗_f+0.12*〖C^2〗_w-2.55* P_i ²
In order to validate the obtained model, two normal probability diagram comparing the predicted data of the model with the real values were used. The results showed that with decreasing flow distribution ratio, particle separation efficiency increases, also separation efficiency decreased with increasing inlet pressure, and with increasing effluent concentration.

Conclusion
In this study, the effect of hydraulic parameters including flow separation ratio, inlet pressure and feed concentration was investigated on the performance of a semi industrial hydro cyclone. The analysis of the results using Response Surface Methodology (RSM) showed the effectiveness of the statistical method for obtain the optimum operational condition of the examined hydro cyclone. Based on the RSM method, the highest separation efficiency was obtained 86 and 88%, for Granite and Marble powder stone respectively.
Key words:
Flow ratio, Hydro cyclone, wastewater treatment, Separation efficiency.