ON NEPHOLOMETRIC STUDY OF PAINT EFFLUENT USING TYMPANOTONOS FUSCATUS EXTRACT

Adsorptive study of paint effluent coagulation using T. fuscatus coagulant (TFC) is investigated. Effects of pH, dose, time, and temperature were investigated. Functional group, crystalline, morphology and thermal characteristics of samples were determined. Equilibrium data were analysed by Langmuir, Freundlich, Temkin, Frumkin, and Dubinin-Radushkevich (D-R) isotherms. Kinetic data were fitted to reversible first order, pseudo-first-order, pseudo-second-order, Elovich, intra-particle diffusion and Boyd kinetic models. Process Gibbs free energy (∆G), enthalpy (∆H) and the entropy (∆S) were evaluated. The process was best described by Langmuir isotherm (R > 0.99; X ˂ 0.6; SSE ˂ 0.7). Pseudo second order best fitted the kinetic data. The process was spontaneous, feasible and endothermic. 97% optimal removal was achieved at pH 5. Tympanotonos fuscatus extract has potential for application as an effective coagulant while showing significant component of adsorptive phenomenon


INTRODUCTION
Industrialization has accelerated pollution in the aquifers, such that much of the water requires a form of treatment before use.Paint effluent (PE) contributes to this pollution.PE is turbid and contains highly toxic compounds that harm humans, fishes and contaminates the food chain if drained into soil [1,2].Thus, the treatment and safe disposal of PE become vital for environmental conservation.
The treatment methods are selective and include chemical precipitation, adsorption, ion exchange and coagulation/flocculation, which had been implemented using varieties of coagulants and effluents [3][4][5][6][7].The advantage is that coagulation is robust, relatively low energy demand, needs low operator skill and active in natural organic matter (NOM), inorganics and turbidity enriched effluent.
Factors that affect coagulation include raw effluent characteristics, temperature, pH, dosage, etc [8].Traditionally, coagulation-flocculation has been achieved using inorganic alum and iron chloride.Problems with their usage include poor performance in low-temperature water and high sludge volume generation and link to Alzheimer's disease in human [9].These problems motivated the use of extracts from snail shell, nirmali seeds (Strychnos potatorum), Moringa oleifera, tannin, cactus [10] and T. fuscatus shell.
T. fuscatus shell (TFS) is of natural non-toxic chitin, which is a major component of the shells of crustacean.It is enriched with carbohydrate biopolymer [11,12].TFS abound as wastes in Nigeria, making it attractive as biomaterials.T. fuscatus coagulant (TFC), obtained by deacetylation of chitin [11,12], has been applied in varying effluents and could be extended to PE.
Currently, there is little study focus on adsorptive component of bio-coagulation, hence this report contributes towards bridging this gap.Coagulation data were analysed in the light of adsorption isotherm, kinetics and thermodynamics.Effects of process variables were evaluated.Instrumental and physiochemical characterization of sample were conducted.

Material characterization
Paint effluent.Standard APHA methods [15] were applied for physiochemical characterization of PE.
T. fuscatus shell.Yield/weight loss, bulk density, ash content, oil content, moisture content and protein content were determined as reported elsewhere [17].

Coagulation and flocculation experiment
Effect of coagulant dosage on efficiency.Initial pH and turbidity of PE were determined.(i) 1000 mL of the PE contained in 10 different 1000 mL GG-17 beakers (10 cm diameter) were dosed with 0.50-5 g/L of TFC.(ii) Using magnetic stirrer, the mixture of the effluent and coagulant contained in the 1000 mL beakers were subjected to rapid mixing at 250 rpm (G = 550 s -1 ) for 2 min, followed by slow mixing at 30 rpm (G = 22 s -1 ) for 20 min.(iii) At the end of slow mixing, the treated PE was allowed to settle for 30 min.(iv) At 30 min settling time, 20 mL of the supernatant was respectively pipetted from 2 cm depth into 50 mL turbidity cuvette and residual turbidity measured for each dosage for the determination of optimum dosage.
Effect of pH variation on efficiency.The optimum dosage obtained from results was used for the evaluation of pH effect.The following steps were involved: (i) Equal optimum dosages of TFC were dosed into 9 different beakers each containing 1000 mL of PE sample.The samples pH was adjusted to 2, 3, 4, 5, 6, 7, 8, 9 and 10 using 0.1 M H 2 SO 4 and 0.1 M NaOH just before dosing of the coagulant sample.(ii) Steps (ii-iv) in the previous subsection were repeated with respect to pH variation, leading to determination of optimum pH.
Temporal variation of Q t with dosage.(i) Steps (i)-(ii) were repeated.(ii) During the settling period following the ceasing of slow mixing, 20 mL of the supernatant was respectively pipetted from 2 cm depth into 50 mL turbidity cuvette at 3, 5, 10, 15, 20, 25 and 30 min.The residual turbidity of each supernatant collected was measured and converted to mg/L on multiplying turbidity by a conversion factor of 2.35 [13].

Analytical method
The adsorptive capacity, q t (mg/g), and the percentage removal, % Rem, were calculated using Eqs. 1 and 2, respectively.
where C o , C t V and M are initial constant effluent concentration (mg/L), effluent concentration at any time, t; volume of effluent (l) and mass of coagulant (g), respectively.

Characterization results
Physiochemical and biological characteristics.Characteristics of TFS and PE along with the regulatory standard are presented in Tables 1 and 2, respectively.Total suspended solid, total dissolved solid and total solid of PE were relatively significant to support coagulation study.Meanwhile, the protein content of TFS was substantial to suggest TFS as precursor.FTIR spectra analyses.FTIR spectrum of TFC shown in Figure 1 exhibits 19 discernable peaks at 600-4000 cm -1 with a threshold of 1.17.In Figure 1, peaks at 3850 to 3593 cm -1 could be attributed to hydroxyl (O-H) groups.Peak at 3296 cm -1 is linked to secondary amide (N-H) groups.Peaks at 2916 and 2850 cm -1 are for aliphatic hydrocarbon.Aliphatic rings (C=C stretching, NH 2 scissoring, azo compound and N-H bending) were peaked at 1634 to 1443 cm -1 .Peaks at 1082, 1068 and 1032 cm -1 are for C-O stretching.Amine and alkyne peaks at 909, 855, 781, 712 and 699 cm -1 are for N-H stretching, NH 2 wagging and twisting, N-H wagging and =C-H bending, respectively [18].
XRD pattern.The XRD pattern of TFC shown in Figure 2 depicts eleven clear peaks.Some of the crystal peaks were shifted towards left-right axes, resulting from expansion or contraction of the sample.The peaks indicated that the atomic structure of TFC was of primit structure.Thermo-gravimetric and differential scanning calorimetric analyses for TFC are presented in Figure 3.The weight loss of the material could result from chemical reaction (decomposition, combustion) and physitransition (evaporation, desorption, drying) [19,20].Figure 3a indicates that the final r Figure 3a, the initial weight loss resulted from the internal moisture and gaseous losses [21].
The second phase weight loss resulted from the decomposition of the labile component in the samples.gravimetric and differential scanning calorimetric analyses.The TGA and DSC curves for TFC are presented in Figure 3.The weight loss of the material could result from chemical reaction (decomposition, combustion) and physitransition (evaporation, desorption, drying) [19,20].Figure 3a indicates that the final residual mass was 3.26 mg (94.1% original weight).In Figure 3a, the initial weight loss resulted from the internal moisture and gaseous losses [21].The second phase weight loss resulted from the decomposition of the labile component in the 3b indicates phase transition involving two eutectic peaks at 37.5-297 enthalpy of 11.4 kJ/mol.The endothermic densification took place at 112.5-187.5 °C (Figure 3b). Figure 3b indicates glass transition temperature within 31.25-37.5 °C for the coiling of carbon chain necessary for spontaneous densification [21,22].Conclusively, Figure 3 suggested thermal operational stability at activation energy of 15.0 kJ/mol.Figure 3b

Factors sensitivity analysis
Effect of TFC dosage on particle removal efficiency.Figure 5 indicates (at natural pH) that the efficiency increased from 4% at 0.5 g/L, peaking at 46.6% for 2 g/L and thereafter decreased to 6% at 5 g/L.The increase resulted from increased supply of coagulant's charged species (mainly +ve charges) that incrementally destabilized the effluent charged species (mainly -ve charges), thus ensuring progressive particle removal as dosage increased from 0.5 to 2 g/L.Furthermore, the decrease after 2 g/L resulted from sustained re-stabilisation following excessive supply of +ve charged species due to overdosing after 2 g/L, up till 5 g/L.At 2 g/L, both charged species equilibrated for optimum performance [8,23].Hence, 2 g/L applied for the effect of pH.
Effect of pH on particle removal at 2 g/L TFC.The effect of pH on efficiency for optimum 2 g/L TFC is depicted in Figure 6. Figure 6 exhibited alternate decrease and increase in efficiency as the pH decreased from 9-2.The pH ranges 3-2 and 8-5 recorded increment in efficiency due to progressive protonation.Conversely, the decrease in efficiency for pH ranges 9-8 and 5-3 could be explained by net +ve and -ve species induced charge reversal, respectively.Charge reversal results in re-stabilization and coagulation retardation.Optimal 97% at pH 5 denoted equilibrium in the provision of opposing ions for point of zero charge [23].Temporal variation of adsorption capacity for TFC in PE.The q t of TFC is shown in Figure 7.It shows that  90% of adsorption occurred between 0-20 min; thereafter q t became constant [21].Meanwhile, Figure 7, demonstrated that q t increased with decreasing dosage and increasing time.At 0.5 and 5 g/L, the highest and the lowest values of q t were respectively, recorded.q t at 0.5 g/L increased from 372 to 471 mg/g for 0 and (20-30) min, respectively.At 5 g/L, q t increased from 230 to 253 mg/g for 0 and (20-30) min, respectively.Figure 6.Effect of pH on particle removal efficiency at 2 g/L.
Figure 7. Temporal variation of q t vs time at varying dosage and pH 5 for TFC in PE.

Kinetic analysis
Table 3 briefly express the applied kinetic equations and the corresponding plots made.Only pseudo second order plot is shown as Figure 8.The parameters are arrayed in Table 4.
Comparison among R 2 shown in Table 4 indicated the following order of variation: pseudo second order > reversible first order > pseudo first order > Elovich.Hence, the pseudo-second order has the best correlation.Figure 8.The pseudo-second order kinetic plot for TFC in PE at 25 °C and pH 5.
The logarithmic form of Eq.7 yields Eq. 8:

2.5g/l
A straight line plot of Eq. 8 with positive intercept is a condition for intra-particle diffusion controlled process.The K id from Figure 9 intercepts are shown in Table 5 for R 2 ˃ 0.95, confirming particle diffusion as a rate limiting step.
Model reliability was tested by diffusion coefficient, D p (Eq. 9) [29,30]: where r 0 (4.1425 x 10 -13 cm) [23] is the average radius of the TFC particles, and t 0.5 (min) is the half-life of the adsorptive process.

Boyd kinetics
Boyd kinetics equations [30] further confirm the rate-controlling step: where q t is adsorption capacity at time, t, q e is adsorption capacity at equilibrium, bt is a mathematical function of F.q t [30].

Isotherm analysis
Table 7 indicates the isotherm models while Figures 10a to c show the equilibrium plots at 25, 35 and 45 °C, respectively.The isotherm data were subjected to linear and non-linear analyses.
The parameters are shown in Table 8.The values of R

Confirmation of favourability of the adsorptive process
Eq. 17 confirms the favourability of the process for Langmuir [29,32]: It is: (i) unfavourable when R L > 1, (ii) linear when R L = 1, (iii) favourable when 0 ˂ R L ˂ 1, and (iv) irreversible when R L = 0.For Freundlich isotherm, it is favourable if n ranges 1-10.Thus R L and n values in Tables 8 and 9 indicate favourability.

CONCLUSION
Particle removal was a function of dosage, pH and settling time.Optimum efficiency of 97% was obtained at pH 5 and 2 g/L.Kinetic data best correlated with the pseudo-second order equation, q t increased with increasing temperature.Equilibrium data fitted the Langmuir model best.Thermodynamics showed endothermic and spontaneous process.The adsorptive process was a significant component in the coagulation process.This was shown by significant fitting of coagulation data to adsorption model equations, coupled with high performance of TFC at the experimental conditions.

Figure 4 .
Figure 3. (a) TGA and (b) DSC of TFC.SEM analyses.The surface morphology of TFC is shown in Figure4.The images in Figure4appear to be white field with porous but irregular network structure.While Figure4aindicates the penetrating pores towards the internals of the sample mass, Figure4bshows the discrete multiple pores of the sample.The prevalence of these pores activated the binding affinity among the coagulant's pores surfaces and effluent's particles.

Figure 5 .
Figure 5. Removal efficiency vs dosage for TFC in PE.

Figure 9 .
Figure 9. Intra-particle diffusion for TFC in PE at 25 °C and pH 5.

Table 3 .
The kinetic equation used for analysis of kinetic data.

Table 4 .
The kinetic parameters evaluated for TFC in PE at 25 °C and pH 5.

Table 7 .
2, chi-square ( 2 ) and sum of square error (SSE) show that the data best fitted with the Langmuir model (R 2 > 0.99,  2 < 1.4, SSE < 1.6).The data were also fitted to linear models (Figures not shown).Table9indicates best fit for the Langmuir (R 2 > 0.99,  2 < 0.6, SSE < 0.8) and followed by Temkin model.Similar results were obtained in this report where Langmuir isotherm dominated.The Q max increased with increasing temperature.Similar results are obtained for K F and B. The isotherm model used for the analysis of the equilibrium data.

Table 8 .
The isotherm parameters obtained from non-linear analysis of TFC in PE at pH 5 for Langmuir,

Table 9 .
The isotherm parameters obtained from linear analysis of TFC in PE at pH 5 for Langmuir,

Table 10 .
Thermodynamics parameters of TFC in PE.