Treatment of waste water by coagulation and flocculation using biomaterials

Solapas principales

Treatment of waste water by coagulation and flocculation using biomaterials

L Muruganandam, M P Saravana Kumar, Amarjit Jena, Sudiv Gulla and Bhagesh Godhwani
School of Civil and Chemical Engineering, VIT University, Vellore – 632014, Tamil Nadu, India.


Abstract. The present study deals with the determination of physical and chemical parameters in the treatment process of waste water by flocculation and coagulation processes using natural coagulants and assessing their feasibility for water treatment by comparing the performance with each other and with a synthetic coagulant. Initial studies were done on the synthetic waste water to determine the optimal pH and dosage, the activity of natural coagulant, followed by the real effluent from tannery waste. The raw tannery effluent was bluish-black in colour, mildly basic in nature, with high COD 4000mg/l and turbidity in the range 700NTU, was diluted and dosed with organic coagulants, AloeVera, MoringaOleifera and Cactus (O.ficus-indica).. The study observed that coagulant Moringa Oleifera of 15 mg/L dose at 6 pH gave the best reduction efficiencies for major physicochemical parameters followed by Aloe Vera and Cactus under identical conditions. The study reveals that the untreated tannery effluents can be treated with environmental confirmative naturally occurring coagulants.

1. Introduction

The ubiquitous use of water in tanneries has caused a serious problem of drainage and disposal of industrial waste water. Effluents from industries are degrading the underground and surface water quality through seepage and discharge into rivers, due to toxic and undesirable chemical constituents present inthem and thus, being a major cause of water pollution throughout the Palar River’s drainage basin [1]. The constituents of tannery waste water are of inorganic, organic and toxic nature and require extensive treatment before discharge to prevent physical, chemical and biological pollution of the scarce water resources [2].

The leather industries in Vellore are mainly concentrated in Ranipet area around the Northern bank of Palar River in to which the water is discarded. Many tanning industries are located in Ranipet area, and the majority of these tanneries are engaged in chrome tanning process. Daily, discharged wastes from all the tanneries in Ranipet industrial zone is disposed into the Palar River. Thus, the effective treatment of tannery effluents is a matter of concern for the preservation of the water resources in the area. A huge amount of research has already been carried out on effluent treatment using different technologies, such as 

flotation, electrochemical treatment, sedimentation, coagulation, filtration, ultrafiltration and reverse osmosis process [3]; [4]; [5]; [6]. Several researchers have used different natural coagulating agents for treating the effluents. Coagulation has been known to us for effluent treatment since the 19th century in England where lime along with combination with calcium chloride or magnesium was used for this purpose[7].

Coagulation and flocculation are usually followed by sedimentation, filtration, and disinfection, in the primary stage, succeeded by chlorination. This method is used worldwide for water treatment before it is finally distributed to the consumers[8]; [9]. Various types of coagulants are used in typical water treatment processes for making the water fit for use by the consumers. These can be classified into inorganic coagulants, synthetic polymers, and biological coagulants[10]; [11].

A part of the existing problem is that the operational procedures at many treatment plants in developing countries are based on arbitrary guidelines, specifically in relation to the dosage of chemicals. Another problem that plagues the developing nations is of a shortage of skilled workers and insufficient laboratory facilities to monitor process parameters required to run the plant. The authors aim to tackle this problem by providing a viable alternative to the current method of wastewater treatment by inorganic salts by usingorganic coagulants which don’t cause harm to the environment in addition to being cost effective and easyto use by the unskilled labourers [12].

Natural coagulants originating from vegetables and seeds were in use for the purpose of water treatment before the wide scale use of chemical salts, but they have not been able to displace the use of chemical salts as the scientific grasp of their effectiveness and mechanism of action was lacking. The usage of biological coagulants has not picked up so far because of the lack of clarity in the method to use them commercially. They have given way to inorganic salts progressively under modernization and survived only in some parts of some developing countries [10]. However, there has been a renewed interest in understanding the activity of natural coagulants for water treatment in most countries[13]; [14].

Over the normal range of water pH (5–9) particles nearly always carry a negative surface charge and because of this, are colloidally stable and resistant to aggregation. Coagulants are then needed to destabilise the particles which are done by adsorbing counter ions to neutralise the charge on particles. It is well known that biological flocculants can play these roles because they have particular bio macromolecular structures with a large number of functional groups which can interact with contaminants [13]; [14]; [15]. The coagulants discussed in this paper are promising bio flocculants for the preservation of environment as well as purification purposes, as reported in recent patents [16] [17].

Numerous mechanisms such as polymer bridging, polymer adsorption and charge neutralization (including electrostatic patch effects), depletion flocculation, displacement flocculation, etc. have been proposed to explain the destabilisation of colloids and suspensions by polymers[18]; [19]; [20]; [21]. Patch flocculation happens when huge molecules with a high charge density adsorb to particles to form positively and negatively charged areas on the particle surface (this results in strong electrical attraction between particles). Polymer bridging happens when long chain polymers adsorb onto the surface of more than one particle, thereby forming strong aggregates of large flocs. For the case where the polymer and the adsorption site are of opposite signs, it is hypothesized that charge neutralization is the mechanism in action. Mechanisms of coagulation/flocculation involved in the removal of dissolved and particulate contaminants using naturally occurring coagulants often cited are charge neutralization, adsorption, precipitative coagulation, bridge formation (related to the high molecular weight of biomolecules) and electrostatic patch [18]; [4]; [22]

From the literature it is known that efficiency of the coagulation/flocculation process depends on the following factors [11]: The origin and the nature of the naturally occurring coagulant like its molecular weight; the process variables such as the type of equipment used, the type of reagent used in conjunction with it, the dosage of the coagulant, the residence time in the jar test apparatus and the rate of rotation; the chemical and physical properties of the pollutants present (such as polarity) and finally the solution like temperature, pH, the zeta potential, the colour, the concentration of the colloidal particles, the presence or absence of impurities (i.e., dissolved salts or trace elements such as ions and chemicals) [16]; [23].

The objective of the study to determine the activity of natural coagulants on the treatment of real effluents comparable with synthetic wastewater. This study aims to extend the previous work and find a viable way to use the naturally occurring coagulants such as Aloe Vera, Moringa Oleifera seeds and Cactus.

2. Methodology

Preparation of Coagulant
The Moringa Oleifera seeds were sourced locally from a vendor. They were air-dried at 45°C for 48 hours. The chaff surrounding the seed kernel was removed and the kernels were ground finely using a blender into powder. This was the coagulant prepared from Moringa Oleifera.

The cactus pads were washed thoroughly and the outer covering along with the thorns was removed to extract the mucilage. The mucilage obtained was then air dried in an oven at 65°C for 24 hours. The dried mucilage was then ground into the powdered form and coagulant was thus prepared.

The Aloe Vera leaves were washed thoroughly followed by draining of aloin by keeping the leaves in the horizontal position and the gel...

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