Research Article

Influence of Sugar Industry Wastewater on Sugarcane Juice Quality and Soil Health

Ghulam Muhiyuddin Kaloi1* and Mehrunisa Memon2

1National Sugar and Tropical Horticulture Research Institute, PARC, Thatta, Pakistan; 2Department of Soil Science, Sindh Agriculture University, Tandojam, Pakistan.

Received | October 22, 2020; Accepted | August 31, 2021; Published | September 22, 2021

*Correspondence | Ghulam Muhiyuddin Kaloi, National Sugar and Tropical Horticulture Research Institute, PARC, Thatta, Pakistan; Email: [email protected]

Citation | Kaloi, G.M. and M. Memon. 2021. Influence of sugar industry wastewater on sugarcane juice quality and soil health. Pakistan Journal of Agricultural Research, 34(4): 766-773.

DOI | https://dx.doi.org/10.17582/journal.pjar/2021/34.4.766.773

Keywords | Sugarcane, Sugar-Industry wastewater, Juice quality, Sugar yield, Soil health

Introduction

Sugarcane is a valued cash crop and plays an important role in the economy of Pakistan. The crop accounted 2.9% in value addition of agriculture and 0.5% in GDP during 2018-19 (NFDC, 2019). Maintaining optimum fiber (11-14%) quality is vital (Lingle et al., 2010). High fiber (>14%) reduces sugar extraction, and low fiber (<11%) encourages lodging and cane pests. Brix content defines the total soluble solids, dissolved sugars and salts including sucrose, reducing sugars, glucose and fructose present in the cane juice (Nawi et al., 2014). It is indefinite indicator of sugar content. The pol is to the only parameter which signifies the actual sugar content in cane. Purity of juice is simply the ratio between brix and pol. Sugar recovery indicates the recoverable sucrose content of cane, while sugar yield depends on cane yield and sugar recovery. Ultimately, sugar recovery depends on the quality of juice produced. The sugarcane yield decreased by 1.8% in 2018-19 over the previous year, while the sugar recovery increased by 4.49% in the same years (PSMA, 2019). However, there is potential to increase the recovery further. Disposal problem of cane and payment difficulties also restricted the acreage of sugarcane. In addition, there are issues related to cost and timely availability of fertilizer. Particularly potassium, which plays an important role in juice quality.

Distillery wastewater is a rich source of macro and micro nutrients. The country has 18 alcohol manufacturing distilleries generating 3.48 million tons of wastewater annually (Kaloi et al., 2017). The wastewater generated after methanation process, termed as treated wastewater (also spentwash, vinasse, etc.) has reduced BOD, COD and salt content than that discharged directly during distillation. The treated wastewater is a rich source of nutrients, particularly potassium, which otherwise is an expensive input for agricultural community. The high salt content (EC 42 dS m-1), BOD (2000 mg L-1), COD (23000 mg L-1) can be reduced by diluting the wastewater to required concentrations (Kaloi et al., 2017; Armengol et al., 2003). Further, the significant amount of N (2425-4680 mg L-1), P (175-181 mg L-1) and particularly K (8441-23750 mg L-1) has been highlighted (Kaloi et al., 2017; Sadiq et al., 2018). By discarding the nutritive rich wastewater in the vicinity of Sugar mills, it is polluting the environment, instead it can fertilize the plants and reduce pollution load. Rath et al. (2011) reported that application of wastewater in addition to inorganic fertilizers increased the sugar recovery and sugar yield by 13-16%. Armengol et al. (2003) reported that K rich diluted wastewater significantly increased sugar recovery in Cuba. The nutrient rich wastewater can be partially supplemented to the expensive input like inorganic fertilizers in a sustainable manner with minimum adverse impacts. The direct use of wastewater showed adverse impact, while diluted wastewater significantly improved crop quality (Jain and Srivastava, 2012; Saini and Pant, 2014).

The main objective of this research was to assess the potential of Pakistani sugar industry wastewater on sugar recovery and yield and overall effect on soil health.

Materials and Methods

A field study was conducted at farm of Matiari Sugar Mills, Matiari, Sindh Pakistan (25.59° N and 68.44° E). The experiment was conducted in a randomized complete block design (RCBD) with 3 replications. The treatments (20) were a factorial combination of five concentrations (0, 5, 10, 15 and 20%) of treated wastewater and four rates i.e. 0 (control), 1/3rd (84 N – 42 P2O5 kg ha-1), 2/3rd (167 N- 84 P2O5 kg ha-1) and full NP (250 N - 125 P2O5 kg ha-1) of inorganic fertilizers besides additional control received full recommended NPK (250 N, 125 P2O5 and 150 K2O kg ha-1). Inorganic fertilizers were applied in the form of urea, diammonium phosphate (DAP) and sulphate of potash (SoP). In each treatment, two budded Setts of CPF-237 variety planted in the plots having 7 m long 5 rows at 0.75 m space. The crop was irrigated with canal water for first two months (4 irrigations), followed by wastewater application (12 irrigations) up to harvest. The wastewater concentrations were separately prepared in plastic barrels and irrigated through siphon outlet. The volume of irrigation was based on 3 acre inch calculated by using irrigator’s basic equation Q×T=A×D (Irrigation Slide Chart 1999). Where, Q is discharge of water in cusec, T for time in hours, A for area in acres and D for depth in inches. The cusec was calculated on the bases of flow of water (18 L per minute from 1” faucet).

Soil samples were collected at two depths; surface (0-30 cm) and subsurface (31-60 cm). The collected soil samples were air-dried after removing debris, roots and leaves etc., crushed gently, ground using wooden pestle-mortar, passed through 2 mm nylon sieve and kept in plastic bottle. Samples then were analyzed by using standard procedures. Soil texture by the Bouyoucos hydrometer method, pH (1:5) with pH meter (GmbH-Model 960), EC (1:5) by using EC meter (Hanana-HI 8033), the organic matter by Walkley-Black method (Tahir and Jabbar, 1985), total nitrogen (N) by Kjeldahl’s method (Jackson, 1958) and phosphorus (P) and potassium (K) by AB-DTPA method (Ryan et al., 2001). Chloride (Cl) and bicarbonate (HCO3) were determined by the methods given in USSL (1954). Sodium adsorption ratio (SAR) was calculated by using the formula SAR=Na+ / [(Ca2+ +Mg2+ /2)] 1/2 (Chopra and Kanwar 1982) and exchangeable sodium percentage (ESP) by using formula ESP = [100 (-0.0126 + 0.01475 x SAR)] / [1 + (-0.0126 + 0.01475 x SAR)] (Richard, 1954).

The samples of wastewater were collected in poly-carbonyl sterilized air-free containers leaving one fourth empty. The labeled samples were stored, immediately packed into ice boxes, brought to the laboratory and kept at 4 °C in refrigerator. The samples of wastewater were analyzed according to standard procedures (APHA, AWWA and WEF, 1998).

Sugarcane was harvested after 12 months (normal maturity period in Pakistan). Ten canes were selected randomly from each treatment, cleaned, tops were removed and labeled properly. The canes were shredded with Fiberator (Model: NOSCF-L4) and pressed in Hydraulic Press Machine (Model: SCF-HP-06) to obtained juice. The extracted juice was analyzed for brix by Digital Refractometer (Model: PR-101 Japan), pol by Polarimeter (Model AA-5 Series, Optical activity, England), purity by the formula given by Yadava (1993) and fiber content by the method described by Chen and Chou (1993). Sugar recovery was calculated by using commercial cane sugar (CCS) formula [3×P/2 (1-F+5)/100 – B/2 (1-F+3)/100] given by Meade and Chen (1977) and multiplied with factor 0.94 (Faqir et al., 2011). Sugar yield was obtained by multiplying CCS% with cane yield (weighed whole plot).

The data was analyzed using two way analysis of variance (ANOVA) and means were separated by least significant difference (LSD) using software program Statistix 8.1 (Analytical Software, 2005).

Results and Discussions

Soil properties

Properties of the experimental soil presented in Table 1 illustrated that sandy clay loam textured soil was slightly alkaline (pH 7.55 and 7.85), non-saline (EC 1.12 and 0.34-dS m-1) and low in Cl (0.86 and 1.25 meq 100-1 g soil) and HCO3 (0.41 and 0.85 meq 100-1 g soil) at corresponding soil depths of 0-30 and 31-60 cm. SAR and ESP were in normal range at both soil depths. Organic matter (0.08-0.21%), Kjeldahl’s N (0.0045-0.0096%), available P (2.65 mg kg-1) and K (43.33 mg kg-1) were low with exception to later two, which were marginal (5.07 mg kg-1) and K (64.55 mg kg-1) at 0-30 cm soil. Soil properties were categorized according to California Fertilizer Association (1980), Foth (1984), Bohn et al. (1985), Soltanpour (1985) and SSDS (1993).

Wastewater properties

All the properties (Table 2) i.e. EC (3.2 to 11.7 dSm-1), HCO3 (49.2 to 248.7 mg L-1), Cl (131.5 to 697.8 mg L-1), TS (2.4 to 12.9 mg L-1), SAR (2.2 to 6.3) BOD (93.9 to 489.6 mg L-1) and COD (2618.0 to 10131.0 mg L-1), organic matter (0.3 to 1.4%), total N (178 to 1075 mg L-1), P (21.7 to 70.3 mg L-1) and K (988 to 5347 mg L-1) of wastewater increased upon increasing concentration from 5-20%.

 

Table 1: Properties of experimental soil.

Parameters		Soil depth (cm)		Categorization Reference
Soil depth (cm)		0-30	30-60
Particle size (%)	Sand	66.98	69.5	Foth (1984)
	Silt	11.95	11.4
	Clay	21.07	19.1
Textural Class		Sandy clay loam
pH		7.55	7.85	SSDS (1993)
EC (dS m-1)		1.12	0.34	Bohan et al. (1985)
Cl (meq 100-1 g soil)		0.86	0.41	-
HCO3 (meq 100-1 g soil)		1.25	0.85	California Fertilizer Association. (1980)
SAR		1.14	1.35	Bohan et al. (1985)
ESP		0.42	0.72	Bohan et al. (1985)
Organic matter (%)		0.21	0.08	-
Kjeldahl N (%)		0.0096	0.0045	-
AB-DTPA P (mg kg-1)		5.07	2.65	Soltanpour (1985)
AB-DTPA K (mg kg-1)		64.55	43.33	Soltanpour (1985)

 

Table 2: Properties of wastewater used for experiment.

Parameters	Wastewater concentrations (%)
	5	10	15	20
pH	8.4	8.3	8.3	8.2
EC (dS m-1)	3.2	7.1	9.4	11.7
Cl (mg L-1)	131.5	292.5	495.1	697.8
HCO3 (mg L-1)	49.2	108.1	178.5	248.7
SAR	2.2	4.9	5.6	6.3
TS (mg L-1)	2.4	5.4	9.1	12.9
BOD (mg L-1)	93.9	210.7	350.1	489.6
COD (mg L-1)	2618.0	5850.0	7990.0	10131.0
Organic matter (%)	0.3	0.6	1.0	1.4
Total N (mg L-1)	178.0	340.0	737.0	1075.0
Total P (mg L-1)	21.7	48.7	59.6	70.3
Total K (mg L-1)	988.0	2194.0	3770.0	5347.0

 

Juice quality parameters

The quality of juice in the form of fiber, brix, pol and purity content was significantly influenced by wastewater application (Table 3 and Figure 1). The fiber content increased from 12.33% in control to 13.16% under 20% wastewater with percent increase of 6.71. While, brix, pol and purity, respectively increased from 22.03, 16.42 and 70.84 in control to 23.36%, 17.91% and 76.67% under 10% wastewater, which registered a respective percent increase of 6.01%, 9.08% and 8.23% over no wastewater treatment. Based on juice parameters and cane yield, the sugar recovery and sugar yield also increased significantly by wastewater application. The sugar recovery and sugar yield increased from 9.73 and 6.86 in control to 12.27% and 11.25 t ha-1 under 10% wastewater application, with a percent increase of 26.02% and 63.89%, respectively.

 

Table 3: F values with significance for juice quality parameters as influenced by wastewater and inorganic fertilizer rates.

Parameters		F value
	Wastewater	Inorganic Fertilizer	Wastewater × Inorganic Fertilizer
Fiber (%)	58.75*	0.70	2.79**
Brix (%)	8.45*	1.37	0.50
Pol (%)	22.85*	3.09*	1.23
Purity (%)	17.15*	1.48	0.75
Sugar recovery (%)	38.94**	0.14	0.84
Sugar yield (t ha-1)	72.26**	3.54*	4.02**

ns= Non-significant, * p > 0.05, ** p > 0.01

 

On the other side, inorganic fertilizers (NP) resulted in significant increase in pol content only. As for full recommended dose of NPK, the fiber (%), brix (%), pol (%), purity (%), sugar recovery (%) and sugar yield (t ha-1) was 11.95, 22.48, 18.12, 79.20, 12.23 and 10.94, respectively. While, the interaction of wastewater and inorganic fertilizers significantly (p≤0.05) influenced the fiber content of juice from 12.65 in control to 13.54 under 20% wastewater and 1/3rd NP fertilizers (84 kg N and 42 kg P2O5 ha-1). Ultimately, the integration of 10% wastewater and 1/3rd of recommended inorganic fertilizers recovered maximum sugar yield of 12.7 t ha-1.

Soil health

The soils of Pakistan are low in fertility mainly due to macronutrients (N, P and K) and organic matter. The N, P and K are most important nutrients utilized by crops in large amount. The ignorance and unawareness has led to a nutrient imbalance in soil and plant.

 

Table 4: F values with significance for soil health as influenced by wastewater and inorganic fertilizers.

Parameters	Soil depth (cm)	F value
		Wastewater	Inorganic Fertilizer	Wastewater × Inorganic Fertilizer
Nitrogen	0-30	114.03*	10.94*	0.31 ns
	31-60	28.30*	11.00*	1.10 ns
Phosphorus	0-30	728.68*	113.83*	6.84*
	31-60	1228.11*	624.04*	131.47*
Potassium	0-30	757.26*	1.90 ns	0.56 ns
	31-60	517.22*	2.53 ns	0.32 ns
Organic matter	0-30	289.94*	6.19*	0.72 ns
	31-60	36.32*	2.82 ns	0.66 ns
pH	0-30	135.29*	6.36*	0.90ns
	30-60	1013.49*	21.84*	5.02*
EC	0-30	56.49*	1.14 ns	0.84 ns
	31-60	76.38*	18.00*	6.24*
Cl	0-30	173.14*	0.99 ns	0.13 ns
	31-60	79.37*	2.13 ns	0.17 ns
HCO3	0-30	1398.68*	0.33 ns	0.59 ns
	31-60	1161.15*	1.23 ns	0.34 ns
SAR	0-30	201.33*	0.20 ns	0.12 ns
	31-60	19.73*	0.08 ns	0.27 ns
ESP	0-30	199.91*	0.19 ns	0.12 ns
	31-60	19.57*	0.08 ns	0.28 ns

ns= Non-sgnificant, * p > 0.05, ** p > 0.01

 

Statistical analysis (Table 4) indicated that effect of wastewater and inorganic fertilizer rates was significant at both soil depths (surface and subsurface), except case of inorganic fertilizers for K at both soil depths and organic matter at subsurface. The integration (wastewater × inorganic fertilizers) was significant only for P.

Data of N, P and K and organic matter is presented in Figure 2a. Nutrient content and organic matter in soil increased with increasing concentration of wastewater. Values of all fertility parameters were higher at surface soil as compared to subsurface. N increased from 0.012 to 0.019%, P 2.98 to 6.48 mg kg-1, K 59.79 to 267.46 mg kg-1 and organic matter from 0.19 -0.35% at 20% wastewater in surface soil. Similarly, the respective nutrients (N, P and K) and organic matter was increased from 0.004, 0.44, 41.0 and 0.10 in control to 0.009%, 1.25 mg kg-1, 65.12 mg kg-1 and 0.14% at 20% wastewater in subsurface soil. As for inorganic fertilizers application, N and P increased with increasing rate of inorganic fertilizers.

 

The statistical analysis of soil properties (Table 4) depicted that wastewater had significant effect (p≤0.05) on pH, electrical conductivity (EC), chlorides (Cl), bicarbonates (HCO3), sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) at both soil depths (surface and subsurface). The effect of inorganic fertilizers and interaction of both (Wastewater × inorganic fertilizers) was significant (p≤0.05) only for pH and EC at subsurface.

The data of soil properties (Figure 2b) indicated that the values of EC, Cl and HCO3 were higher at surface soil, while, pH, SAR and ESP at subsurface soil. Furthermore, that the values of all soil properties increased with increase in wastewater concentration except SAR and ESP. pH, EC (dS m-1), Cl (meq 100 g-1) and HCO3 (meq 100 g-1) increased from 8.01, 0.98, 0.75 and 1.88 at concentration of 5% to 8.58, 1.40, 1.42 and 3.30 at 20% wastewater, with a percent increase of 7.12, 41.91, 87.92 and 75.22, respectively in surface soil. Similar trend was noted at subsurface soil. Unlike other properties, the SAR and ESP decreased from 2.63 and 2.56 in control to 1.44 and 0.86 with a percent decrease of 45.20 and 66.25, respectively at 20% wastewater in surface soil. Similarly, SAR and ESP were decreased at subsurface soil.

 

The soil under experiment was low in fertility (Table 1). All properties (EC, Cl, HCO3, SAR, TS, BOD, COD, N, P, K and organic matter) of wastewater increased with concentration except pH (Table 2). The results were supported by various workers who analyzed wastewater at various concentrations (Kumar and Chopra, 2013; Adhikary, 2014; Ali et al., 2015). Application of wastewater increased juice quality and sugar yield up to 15% concentration. The concentrated wastewater (20%) reduced same parameters except the fiber. Highest increase was noted at 10% wastewater which increased brix, pol, purity and sugar recovery by 6.01, 9.08, 8.23 and 26.02%, respectively and ultimately the sugar yield by 63.89% over control (0% wastewater). The fiber was in optimal range (11-14%) at all wastewater concentrations (5 to 20%). The fiber is only a parameter needed in an optimal range and either low or high affects the juice quality. In case of inorganic fertilizers rates, the fiber was improved at full rate, while brix and pol at 2/3rd rate. The purity and sugar recovery was better at full rate of inorganic fertilizers. The interactions (wastewater × inorganic fertilizers) of 5 and 10% × 0, 1/3rd, 2/3rd & Full inorganic fertilizers and 15% × 0 & 1/3rd inorganic fertilizers increased sugar recovery between 25-53%, however the difference was statistically non-significant. As for sugar yield, interaction of 10% wastewater × 2/3rd inorganic fertilizer gave an increase of 139.62%. The improvement in quality parameters and sugar yield at 10% wastewater might be due to low salt contents and reduced BOD and COD of wastewater. The initial nutrient requirement for growth was fulfilled by inorganic fertilizers and latterly by wastewater throughout growing period. The concentrated wastewater (15 and 20%) might have high level of salts, BOD and COD that caused salt accumulations and osmotic pressure within the root zone. Concentrated wastewater affected vegetative growth and sucrose formation in plant (Ramana et al., 2001; Rathore et al., 2000). The results were supported by Pujar (1995) and Silvaloganathan et al. (2013) who reported that 10% wastewater significantly improved brix, pol, purity and sugar recovery. However, Matibiri (1996) reported 61.33% increase in sugar yield at 2% wastewater. In contrast, Ashutosh (2014) during three year study reported that sugar yield was better at 75% wastewater × 25% inorganic fertilizer which increased sugar yield by 31.86, 24.72 and 27.64% at first, second and third year crops, respectively.

Soil physico-chemical properties (pH, EC, Cl, HCO3, SAR and ESP) and nutrients (N, P and K) were increased with wastewater concentration except SAR and ESP. The effect of wastewater (5-20%) application was minor on soil pH. It increased between 0.01-7.12%. Armengol et al. (2003) reported 0.65% increase in pH at 5% wastewater. While, Patil and Patil (2013) reported 9.9% increase in pH during one time application of 100% wastewater. The application of 5 and 10% wastewater increased EC by 3.29 and 9.61%, respectively as compared to 20% wastewater which increased EC by 41.91% at surface soil. It might be due to salts like Ca, Mg, Na, Cl and K present in the wastewater. The K might be the major contributor of increase in EC. Sivaloganathan et al. 2013 reported that wastewater contained large amount of soluble salts which increased EC in soil. Similarly, Cl and HCO3 increased between 9 to 90%. Patil and Patil (2013) reported 14% increase in Cl by one time surface application of concentrated wastewater. While, Adhikary (2014) recorded 129% increase in Cl and 215% in HCO3. Unlike other parameters, the SAR and ESP reduced regardless of concentration at both soil surfaces. It reduced between 28 to 65%. Various workers reported reclamation quality of wastewater in sodic soils (Valliapan et al., 2001; Mahendra et al., 2010). It might be due to leaching of Na by Ca and S present in wastewater (Rath et al., 2010). As for soil fertility, the wastewater significantly improved soil organic matter at surface soil. It increased by 38.94, 47.43, 54.19 and 77.53% at 5, 10, 15 and 20% wastewater, respectively. The N, P and K were increased by 5.93, 24.19 and 214% at 5%, 24.58, 31.64 and 232% at 10%, 51.69, 80.41 and 295% at 15% and 67.80, 117.48 and 347 at 20% wastewater, respectively. This might be due to high organic matter and N, P and K content in available form. Chopra et al. (2013) and Patil and Patil (2013) reported that wastewater significantly enriched the soil fertility. It contains large quantities of organic matter (Selvamurugan et al., 2013; Kamble et al. 2016) and N, P and K (Shenbagavalli et al., 2011).

Conclusions and Recommendations

Study concludes that the integrated use of 10% wastewater with 2/3rd of inorganic fertilizers gave more sugar recovery (12.3%) and sugar yield (12.70 t ha-1). Application of 10% wastewater supplemented Urea (N) and DAP (P) fertilizers by 33% and SoP (K) by 100%. Hence, input cost against the fertilizers reduced by 62.82%. This treatment combination improved soil organic matter by 53%, Kjeldahl’s by 50%, AB-DTPA P and N by 119% and 243%. It may be the partial substitution of costly inorganic fertilizers, potassium (K) in particular. It was therefore concluded that the application of sugar industry wastewater at 10% along with 2/3rd dose of nitrogen and phosphorus was recommended for sugarcane.

Acknowledgment

The authors are grateful to management of Matiari Sugar Mills for their support in providing wastewater (distillery) and related material to conduct experiment on their field.

Novelty Statement

Sugarcane based wastewater, rich in nutrients can be better utilized to fertilize the crop itself, rather than polluting the environment.

Author’s Contribution

Ghulam Muhiyuddin Kaloi: Conducted physical experiments, collected data, laboratory analysis, statistical analysis and prepared manuscript.

Mehrunisa Memon: Conceived the idea of this research, developed methodology, lab testing of wastewater, reviewed the manuscript, gave technical input thought.

Conflict of interest

The authors whose names are listed certify that they have no any “conflict of interest” in the subject matter or materials discussed in this manuscript.

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