INDUSTRIAL WASTE UTILIZATION FOR LAND RECLAMATION AND CROP PRODUCTION

Application of Untreated Distillery Effluent (Spentwash) for the Reclamation of Sodic Soils

Amendments generally used to reclaim sodic soils are gypsum, phosphogypsum, iron pyrites and elemental sulphur. All these are inorganic in nature. Some of the organic amendments to reclaim the sodic soils are press-mud, farmyard manure (FYM), coir dust and green manures. The direct discharge of untreated distillery effluent (spentwash) to reclaim and improve the productivity of the sodic soils is now advocated. Untreated distillery effluent (spentwash) is acidic (pH: 3.8 – 4.2) with considerable quantity of potassium, calcium and magnesium and traces of micronutrients. Organic compounds, mainly the humic related melanoidins improve the bio-catalytic potential of the treated soil.

Hence, only one time application of 3.75 to 5.00 lakhs litres of untreated distillery effluent (spentwash) per hectare of sodic soils in summer months is recommended. Natural oxidation can be induced for a period of six weeks with two intermittent dry ploughing at a particular interval. Then, after 45 – 60th day of application, soil is to be irrigated with fresh water and drained. This treatment reduces the pH and exchangeable sodium percentage to normal level and increases the productivity of the sodic soils. After this reclamation practice, rice crop can be raised in the effluent applied field adopting the conventional cultivation technique. Application of this effluent again to the next crop/season or year after year and also to the land nearby drinking water sources is not advocated.

Application of Treated Distillery Effluent to Crops

Irrigation of Pulp and Paper Mill Effluents          

Pulp and paper effluents contain lot of dissolved solids and stabilized organic matter.  The properly treated effluent with EC less than 1.2 dSm-1 as such can safely be used for irrigation with appropriate amendments viz., pressmud @ 5 tonnes ha-1 (or) fortified pressmud @ 2.5 tonnes ha-1 or daincha as in -situ green manure
(6.25 tonnes ha-1).

Though there were perceptible changes in soil pH, EC, available NPK, exchangeable cations, exchangeable sodium per cent and sodium absorption ratio, there is no detrimental effect due to sodium either on soil or plants grown in sandy loam soils with good drainage facilities. This treated effluent can be used for irrigation in these soils for the following crops and varieties along with recommended doses of amendments viz., pressmud @ 5 tonnes ha-1, or fortified pressmud @ 2.5 tonnes ha-1 or daincha as in situ green manure (6.25 tonnes ha-1).

However, irrigating this treated effluent to oil seed crops like gingelly and castor, pulses like greengram and blackgram is not advocated as they were found to be sensitive for this type of effluent irrigation.

Crops and Varieties Suitable for Tannery Waste Affected Soils

Based on the results of field trials conducted at Vellore district, the following crops, trees and their varieties are recommended for the tannery waste affected soils

            Crops                                       Varieties
            Cereals                        : Rice (TRY 1, CO 43, Paiyur 1, ASD 16)
            Millets                         : Ragi (CO 12, CO 13)
            Oilseeds                      : Sunflower (CO 4, Morden) and Mustard
            Cash crops                  : Sugarcane (COG 94076, COG 88123, COC 771)
            Vegetables                  : Brinjal, Bhendi, Chillies, Tomato (PKM 1)
            Flowering crops            : Jasmine, Neerium, Tuberose
            Trees                           : Eucalyptus, Casuarinas and Acacia

Reclamation of papermill effluent irrigated soil

Application of 7.25 t ha-1 of gypsum is recommended to reclaim the TEWLIS area soils of Karur district (Moolimangalam, Pandipalayam, Pazhamapuram, Thadampalayam and Ponniagoundanpudur) where the treated paper mill effluent is being continuously used for irrigation since 1995.

Application of pressmud @ 6 t ha-1 along with Blue Green Algae (15 kg ha-1) and Gypsum (50% Gypsum requirement) is also effective in reclaiming the saline sodic soil with continuous papermill effluent irrigation and to increase the green fodder yield of Lucerne.

TNAU constructed wetland technology

TNAU constructed wetland technology is recommended for treating the papermill effluent using species viz., Typha latifolia, Pharagmitis australis and Cyperus pangorei with plant density of 2.5 lakhs shoots/ ha (25 shoots m-2).  Around 1 ha of wetland area is required to treat 1000 m3 of wastewater per day with a retention time of 2 – 3 days.

The wetland beds should be lined with an impermeable liner made of PVC or high-density poly ethylene (HDPE).  The bottom most layer of wetland should be filled with ½ to 1” pebbles to a depth of 6 cm followed by Pea gravel of 6 cm, coarse sand and fine sand each of 7 cm and the top layer with soil to a depth of 9 cm.

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