Effect of Biomethanated Spent Wash on Enzymatic Activities under Irrigated Condition

Molasses, one of the important byproducts of the sugar industry, is the chief source for the production of ethanol in distilleries by fermentation method. The Indian distillery units mainly use sugarcane molasses as a preferred raw material because of its easy and large-scale availability.

Alcohol is produced from molasses by two types of fermentation processes i.e., Praj type and Alfa Laval distillation. In Praj type, for the production of one liter of alcohol, about 12–15 liters of spentwash is generated; whereas, in the Alfa Laval continuous fermentation and distillation process, only 7–8 liters of wastewater per liter of alcohol is produced; where, it uses evaporators for concentrating the effluent.

The spentwash is acidic (pH 3.94 - 4.30), dark brown liquid with high BOD (45,000 – 1,00,000 mg l⁻¹), COD (90,000 – 2,10,000 mg l⁻¹) and produces obnoxious odor. Although it does not contain toxic substances, its discharge without any treatment brings about immediate discoloration and depletion of dissolved oxygen in the receiving water streams, in turn posing a serious threat to the aquatic flora and fauna (Mane et al., 2006).

Distillery waste is rich in organic matter and nutrients, especially nitrogen and potassium, and also can be utilized as a source of irrigation water in water-scarce areas. However, they are also characterized by high soluble salts coupled with high BOD and COD. Hence, while aiming for better crop production, their utilization has to be optimized for sustaining the environment.

On average, distillery effluents release 80 million kg of nitrogen and 520 million kg of potassium annually. Thus, the availability of nutrients in distillery effluents and the possibility of substituting these for inorganic fertilizers in agriculture have great promise (Joshi and Singh, 2010). The addition of organic matter through the BDS may be favorable for enzymes in soils.

Batch et al. (1993) observed that the spentwash at 250 m³ ha⁻¹ rate stimulated the soil microorganisms and increased the dehydrogenase activity in soil. The spentwash addition increased the phosphatase, dehydrogenase, and urease enzymes in dry land black and red soils, especially at levels of 125 m³ ha⁻¹ (Murugaragavan, 2002).

A field experiment was conducted at Research and Development Farm, The Sakthi Sugars Pvt. Ltd., Appakkudal, Erode District, Tamil Nadu in a randomized block design with three replications using sesame (Sesamum indicum) var. VRI (Sv) 2 as the test crop. The experimental field was laid out, and the calculated quantity of BDS (Table 1) was uniformly applied in each plot as per the treatment details given below. Then, the soil was ploughed at 10-day intervals to provide better soil aeration and consequent reduction of BOD level in the soil-water system.

Treatment Details

• T₁: Absolute control
• T₂: Control - 100% recommended dose of NPK
• T₃: 25% N through DSW and 75% N through an inorganic source based on crop requirement
• T₄: 50% N through DSW and 50% N through an inorganic source based on crop requirement
• T₅: 75% N through DSW and 25% N through an inorganic source based on crop requirement
• T₆: 100% N through DSW

While applying P, the available P in DSW and inorganic P has been taken together to meet the P requirement of the crop. Potassium has been skipped in DSW-applied treatments.

Soil samples were collected at 30 (R₁), 60 (R₂), 90 (R₃), and 120 DAS (R₄). The activities of urease, phosphatase, and dehydrogenase enzymes were assayed as per the standard procedures (Tabatabai and Bremner, 1972).

Results and Discussion

Dehydrogenase Activity

The DSW application increased the activities of dehydrogenase, phosphatase, and urease with different doses of DSW viz., 75 per cent N through...

Table 1. Characteristics of Post Methanated Distillery Spentwash (PMDSW)

Physical Properties

Physico-Chemical Properties

Water Soluble Cations

Water Soluble Anions

Other Properties

Biological Properties

DSW + 25 per cent N through inorganic source in the field experiments with sesame under irrigated conditions, respectively. The dehydrogenase activity of the soil was also influenced by other doses of DSW application. Significantly higher dehydrogenase activity of 29.92 and 24.87 μg of TPF g⁻¹ of soil was recorded in T₆ and T₅, which were on par with each other. The lowest enzyme activity of 11.70 μg of TPF g⁻¹ of soil was recorded in T₁ (Control).

The soil dehydrogenase activity significantly differed at all stages of crop growth. The dehydrogenase enzyme activity was found to be the lowest at S₄ (harvest stage) with 20.05 μg of TPF g⁻¹ of soil and the highest at S₁ (vegetative stage) with 23.35 μg of TPF g⁻¹ of soil (Fig 1).

Fig 1. Effect of distillery spent wash application on soil dehydrogenase activity Phosphatase activity The phosphatase activity of the soil was highly influenced by different doses of DSW application. Significantly higher phosphatase activity of 15.07 µg of PNPP g-¹ of soil was recorded in T (100 per cent N through distillery spentwash) followed by the treatments T5, T₄ and T3. The lowest enzyme activity of 9.62 µg of PNPP g¹ of soil was recorded in T, (Control). The soil phosphatase activity significantly differed at all stages of sesame crop growth. The enzyme activity was the lowest at S, (harvest stage) of 11.00 µg of PNPP g¹ of soil and the highest at S 1 (Vegetative stage) of 12.15 µg of PNPP g¹ of soil (Fig 2).

Fig 1. Effect of Distillery Spent Wash Application on Soil Dehydrogenase Activity

(ϻg TPF g⁻¹ of dry soil h⁻¹)

Fig 2. Effect of Distillery Spent Wash Application on Soil Phosphatase Activity

(ϻg P-NPP g⁻¹ of dry soil h⁻¹)

Urease Activity

Urease activity of the soil was measured in distillery spent wash-applied fields. Significantly higher urease activity of 10.97 μg of ammonia released g⁻¹ of soil h⁻¹ was recorded in T₅ (75% N through distillery spent wash + 25% N through inorganic source), which was on par with T₆ (100% N through distillery spent wash) of 10.80 μg of ammonia released g⁻¹ of soil h⁻¹. The lowest enzyme activity of 5.62 μg of ammonia released g⁻¹ of soil h⁻¹ was recorded in T₁ (Control).

The soil urease activity significantly differed at all stages of crop growth. The enzyme activity was the lowest at S₄ (harvest stage) with 8.95 μg of ammonia released g⁻¹ of soil h⁻¹, and the highest at S₁ (vegetative stage) with 9.81 μg of ammonia released g⁻¹ of soil h⁻¹ (Fig 3).

Fig. 3. Effect of distillery spentwash application on soil urease activity This might be due to tremendous increase in the microbial population, availability of most of the essential nutrients and organic carbon content of the soil applied with different levels of DSW. This is in close agreement with the findings of Kamalakumari and Singaram (1995), who observed a strong positive relationship among the available NPK and organic carbon for enzyme activities of the soil. The work of Goyal et al. (1995) and Rajannan et al. (1998), Murugaragavan (2002) lend support for the increased activities of soil enzymes owing to the addition of spentwash. Similar results were obtained by Sivashankari (2009) and Nandha Kumar (2009).

The results of the present study indicated that the application of post-methanated distillery spentwash increased the enzyme activities of the soil throughout the crop growth period of sesame. The enzyme activities viz., phosphatase, dehydrogenase, and urease recorded the highest values of:

• Phosphatase: 15.07 μg p-nitro phenol g⁻¹ soil h⁻¹
• Dehydrogenase: 29.92 μg TPF g⁻¹ soil h⁻¹
• Urease: 10.97 μg NH₄-N g⁻¹ soil h⁻¹

These highest values were observed in the treatment T₆ (100% N through distillery spentwash) and T₅ (75% N through DSW and 25% N through inorganic source), respectively, under irrigated conditions.

Enhancement of phosphatase, dehydrogenase, and urease enzyme activities was observed in the soil that received different doses of post-methanated distillery spentwash, maintaining stable enzyme activities till the harvest stage of the crop.