Materials and methods
Materials
Hydrated aluminium sulphate [Al2(SO4)3] manufactured by
Feralco UK Ltd and Magnafloc155 (Anionic polyacrylamide) by
Goldcrest Chemicals Limited were used as coagulant and flocculant
respectively. Sulphuric acid (H2SO4) manufactured by Brenntag
and lime solution [Ca(OH)2] by Tarmac were used for regulating
the pH value of effluent during the treatment processes. The details
of used materials are described in Table 1.
Sampling
The effluent samples were collected from the polymer
manufacturing plant at Scott Bader Company Limited situated in
Northamptonshire, UK. The samples were collected from the outlet
of the holding tank where the effluent is stored before it is sent to
the effluent treatment plant.
The initial solid contents in the effluent samples collected were
1.0% on dry basis. Various characteristics of the effluent were
determined according to the Standard Methods [36] and are
summarised in Table 2. The target values are defined for Scott
Bader as the discharge consent limits by Anglian Water (regulated
under the Water Industry Act 1991).
Jar tests
The jar test has been the standard technique used to optimise
the addition of coagulants and flocculants used in the water and
wastewater treatment industry from more than half a century. The
scope of this practice is to evaluate the treatment to reduce the
suspended, colloidal and non-settable matter from the effluent by
chemical coagulation–flocculation. The same standard was utilised
to evaluate the variables normally encountered in the coagulation–
flocculation process [13].
Considering the number of possible jar tests and total effluent
volume of 15 L available for all these tests, it was decided to use
200 mL sample for each jar test. The resulting optimal pH and dose
of chemicals were then applied to 500 mL and 1000 mL of the
remaining sample and the same results were observed as those for
200 mL. The equipment used was a laboratory flocculator model
JLT-4 VELP by Scientifica, Italy equipped with four parallel beakers.
A volume of 200 mL of the polymer effluent was placed in each
beaker. The desired pH for coagulation was adjusted using
sulphuric acid (H2SO4) and for flocculation using lime solution
[(Ca(OH)2]. Inorganic coagulant aluminium sulphate [Al2(SO4)3]
and anionic polyacrylamide flocculant (Magnafloc155) were used
in different combinations.
For coagulation, vigorous mixing at 200 rpm was used for 5 min
whereas for flocculation, slow mixing at 40 rpm was used for 5 min
followed by settling time of 30 min. Two series of jar tests were
conducted according to the standard test methods [37]. In the first
series, the dose of coagulant and flocculant was varied from 0.5 to
2.5 mL. In the second series, the pH for coagulation was varied from
Table 1
Materials characteristics.
Chemicals Formula Physical form Molecular weight (g/mole) Concentration (%) Purpose
Sulphuric acid H2SO4 Liquid 98.01 77 pH adjustment
Aluminium sulphate Al2(SO4)3 Powder 342.15 26 Coagulant
Lime Ca(OH)2 Powder 74.093 12 pH adjustment
Magnafloc155 –C3H5NO– Powder 5 106 0.16 Flocculant
Table 2
Physico-chemical characteristics of the pre-treated effluent.
Parameters Units Initial values Target values
Temperature 8C 45 20,000