© 2017 IJSRST | Volume 3 | Issue 3 | Print ISSN: 2395-6011 | Online ISSN: 2395-602X

Themed Section: Science and Technology

Coagulation for Wastewater Treatment : A Review on Investigations and

Studies
Sunil Jayant Kulkarni
Chemical Engineering Department, Datta Meghe College of Engineering, Airoli, Navi Mumbai, Maharashtra, India

ABSTRACT

Chemical treatment of wastewater can be carried out with the help of different coagulants, flocculating and
precipitating agents. Coagulation is one of the most important chemical treatments. Various investigators have
carried out investigation on coagulation aimed at studying selection of coagulant, optimization of affecting
parameters and combinations with other treatment methods. Current review is aimed at summarizing research and
studies on coagulation. Many investigators recommended use of polymer-based coagulant. Coagulants like chitosan
and moringa seeds indicated good coagulation properties. Coagulation combined with ultra- or microfiltration
improved the treatment process of water with higher organic matter load. Selection of coagulating agent and proper
combination of coagulation with other physicochemical treatment can lead to highly effective, economical and
efficient solution for wastewater treatment.
Keywords: Coagulant, Particle Size, Membrane Separation, Hybrid Method, Removal, Suspended Matter.

I. INTRODUCTION flocculating and precipitating agents. Coagulation is one

of the most important chemical treatments. Various
Wastewater treatment in chemical, pharmaceutical, paint, investigators have carried out investigation on
cement, mining, petroleum and many other industries is coagulation aimed at selection of coagulant,
becoming important area of research due to increasing optimization of affecting parameters and combinations
awareness about pollution and scarcity driven need for with other treatment methods. Current review is aimed
recycle. The domestic wastewater treatment is also at summarizing research and studies on coagulation.
major concern for civil society. The conventional
treatment plant contains primary treatment with screens, II. COAGULATION FOR WASTEWATER
primary sedimentation and other physical treatment TREATMENT: A REVIEW ON INVESTIGATIONS
steps. The secondary treatment contains biological AND STUDIES
treatment. The biological treatment methods are divided
into suspended growth and attached growth processes. Zueva et.al studied coagulation treatment for wastewater
Activated sludge process is widely used biological of meat industry [15]. They carried out experiments on
treatment method [1-4]. In this the organic matter is wastewater treatment with coagulants and so coagulant
stabilized. The biological treatment can be aerobic and aids. They considered the meat industry wastewater as a
anaerobic. Anaerobic method reduces space requirement dispersed system (suspension). They observed that
and produces methane gas, which has fuel value [5-8]. Aluminum sulfate at low pH (<7, 8) form positively
Trickling filter treatment is important attached growth charged sol of aluminum hydroxide. It neutralized
method [9, 10]. The membrane separation methods are negatively charged particles in wastewater as above pH
costly but effective [11, 12]. The membrane separation 7 nano-particles in a sol-gel system are charged
methods are normally used as tertiary or higher negatively. For aluminum sulphate, the fats removal was
treatment methods in treatment train. Adsorption can be much more effective than adsorption of iron salts. They
used for removal of various pollutants from wastewater used an inorganic sorbent and alumnum sulfate jointly
[13,14]. Chemical treatment of wastewater can be to increase the value of Zeta potential and the
carried out with the help of different coagulants, effectiveness of purification almost twice. According to

IJSRST1733182 | 10 April 2017 | Accepted: 22 April 2017 | March-April-2017 [(2)3: 501-505]

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them, dual aluminum sulfate – alumina systems can conditions, 100% removal of total coliforms, E. coli,
markedly enhance coagulation at a much lower dosage. Giardia and Cryptosporidium was obtained due to a
hygienic barrier effect .They concluded that chitosan
Jin carried out investigation on use of a high resolution and Moringa oleifera have a potential application as
photographic technique for studying natural coagulants in CF-MF/UF hybrid processes.
coagulation/flocculation in water treatment [16]. Marble processing wastewater was treated by
Generally a microscopic image technique is used in the coagulation/flocculation /Sedimentation methods by
coagulation and flocculation process. According to them Domopoulou et.al.[20]. They investigated the optimum
the sample handling disturbs the floc characteristics conditions for the maximum solid waste removal. In
during measurement. To evaluate flocculation processes, their investigation they examined hydrated metal salts
they proposed a high resolution photographic technique. includingAl2(SO4)3 ,.18H2O, FeCl3.6H2O and
By using this technique, they obtained images of flocs FeSO4.7H2O for their turbidity removal capacity under
directly while the flocculation process was taking place. various dosages. According to the jar test carried out by
By using camera control software and particle size them FeCl3.6H2O presented the highest turbidity
analysis software, this method provided a convenient removal ability. FeSO4.7H2O exhibited poor results.
means of gathering data to calculate size distribution.
Angreni carried out review on optimization of A review was carried out by Ghernaout and Boucherit
conventional drinking water treatment plant [17]. for natural organic matter (NOM) removal from water
According to them overdosing in coagulation can be [21]. Instant and efficient dispersion of coagulant
avoided by using jar test. Fouling or clogging of species into raw water is objective behind rapid mixing.
injectors or diffusers and side reactions are other According to them mechanical mixing is not sufficient
problems in coagulation. Intra cell baffles and tapered for an instantaneous and uniform coagulant dispersion.
coagulation can minimize these problems. They divided They proposed pump diffusion mixer (PDM) for this
parameters into two groups, raw water quality and purpose. They found that at lower coagulant dosage, in-
parameters relative to conditions of process. A Review line hydraulic jet and static mixers were able to achieve
on applications of coagulation flocculation and ballast performance equivalent to that of the mechanical mixing
flocculation was carried out by Borchate et.al.[18]. type. According to them, chemical coagulation(CC)
According to these studies the use ballast flocculation using in-line hydraulic jet mixer such as pump diffusion
serves for floc formation and ballast to increase floc mixer, PDM was a reasonable method for the
density and settling velocity. It can reduce clarifier improvement of coagulation process. Hassanien carried
surface area. In this process, micro floc particles are out investigation on physic chemical treatment of
formed with a specific gravity of greater than two. This water[22]. He attempted improvement in the quality of
process uses continuously recycled media and a variety town water by application of alternating current, direct
of additives to improve the settling properties of current and magnetic field . He used these methods as
suspended solids. In this processes ferric sulfate, an pre-treatment to enhance the coagulation and
anionic polymer can be used as coagulants, and a ballast flocculation. In his investigation he observed that
material such as micro sand, a micro carrier, or coagulation of natural colloids and other material
chemically enhanced sludge can be employed. suspended in water was faster in water impacted by an
electric current. Also he found that there were small
Bergamasco et.al. carried out investigation on changes in pH, total dissolved solids, conductivity and
coagulation/ flocculation and membrane filtration temperature of water after treatment. The considerable
hybrid process for water treatment[19]. They used decrease was obtained in the parameters like turbidity,
natural coagulants like chitosan and moringa seeds. total suspended solids and hardness.
They combined coagulation process with membrane
filtration process (micro and ultrafiltration).They Bahadori et. al. studied coagulation and flocculation
observed that permeate quality was increased as process design [23]. The effect of these two processes
compared to individually operated systems. Also the causes’ small pollutant particles such as metals to
study indicated that applying CF-MF/UF at optimum aggregate and form large enough floc. According to

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them, three types of coagulants are electrolytes, organic opinion, the important disadvantage of the coagulation is
polymers and synthetic polyelectrolytes. They also generation of large quantities of chemical sludge and its
discussed choice of coagulant. According to them, the classification as hazardous waste. Coagulation can bring
type and quality of water, variations in the quality of the about solids removals of about 90% as compared to
raw water, quality requirements and use of the treated about 35% without coagulation ahead of gravity settling.
water, nature of the treatment after coagulation and
degree of purity of reagents are determinants in choice Desai and Sahu carried out comparative study of
of coagulants. Sostar-Turk et.al. carried out investigation
polymer and regular coagulant [28]. They treated
on coagulation and membrane filtration processes for municipal wastewater. In their studies they found that
laundry wastewater treatment [24]. They carried out polymer-based coagulant and flocculent agent was able
wastewater treatment with conventional method with to achieve turbidity removal (almost 100%, depending
precipitation/coagulation and the flocculation process on the dosage) and around 50% of BOD5 and COD
with adsorption on granular-activated carbon (GAC). removal. They concluded that polymer-based coagulant
They also proposed alternative method with membrane and flocculent agents were quite effective coagulant and
filtrations, namely ultrafiltration (UF) and reverse flocculent agent. They also found that sludge production
osmosis (RO). Their analysis of untreated water was reasonably within normal ranges. Farhaoui and
indicated that temperature, pH, sediment substances, Derraz reviewed optimization of drinking water
total nitrogen and phosphorous, COD, BOD5 and the treatment process[29]. According to them optimization
amount of anion surfactants were above the regulatory can decrease the managing and monitoring expenses and
limits. They found that permeate coming from RO met improve the quality of the produced water. They
the required regulation as well as requirements for proposed the use of sludge as coagulant aid with the
reusing in washing process. The limiting factor was the aluminum sulfate. It can reduce aluminum sulfate
cost of membrane processes compared to the GAC dosage. By using this approach, the aluminum sulfate
treatment process. dose required was reduced to 40% of the conventional
requirement. Also it reduced the sludge volume. The
Prakash et.al. treated waste water by coagulation and combination of coagulation and low-pressure membrane
flocculation [25]. According to them, there is filtration was used by Konieczny et.al. for wastewater
considerable variation in properties such as source, treatment [30]. They used UF/MF and a hybrid process
composition charge, particle size, shape, and density. In coagulation–UF/MF. They used capillary modules
their investigation they used coagulants such as alum, made of polyethersulfone (PES) for ultrafiltration and of
ferric chloride and ferrous sulphate. They carried out polypropylene (PP) for microfiltration. Iron chloride
experiments under optimum conditions of pH and (FeCl3·6H2O) and aluminum sulfate (Al2(SO4)3·18H2O)
coagulant dosage. They found that alum was most were used as coagulants. The hybrid treatment included
efficient with removal percentage of 98.9. The optimum coagulation–sedimentation–MF/UF and in-line
pH value for treatment was 7. Farajnezhad and Gharbani coagulation (without sedimentation)–MF/UF systems.
used poly aluminum chloride and ferric chloride as They observed that coagulation combined with ultra- or
coagulants for petroleum wastewater treatment [26]. microfiltration improved the treatment process of water
They observed that poly aluminum chloride was more with higher organic matter load. According to these
efficient. Also the flocs formed by poly aluminum studies, in-line coagulation arrangements were more
chloride were larger than flocculated formed by ferric effective. This arrangement saved space and also
chloride. The research also indicated that pH had no reduced the amount of coagulant used. Ahamad et.al.
significant effect on color removal of petroleum used coagulation and flocculation processes for
wastewater. Sahu and Chaudhari reviewed chemical separating the suspended solids portion from water[31].
wastewater treatment used for industrial wastewater [27]. They studied the impact of pre-sedimentation on
According to them use of inorganic salts and polymeric optimum coagulant dosage. They determined optimum
organic coagulants is common for potable water. alum doses at optimum pH and alkalinity.
According to them, the most important factor in
coagulation is the selection of coagulation. In their III. CONCLUSION

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