MSc

The study entitled “Evaluation of sewage sludge as a growth medium for ornamentals” was carried out in the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani during 2015-2017. The main objectives of the study were to characterise the sewage sludge generated from sewage treatment plant, Muttathara and to evaluate its suitability as a growing medium for ornamentals.
The study involved two separate phases. In the first phase sewage sludge samples were collected from the Muttathara treatment plant and it was analysed for physical (bulk density, water holding capacity and porosity), chemical (pH, EC, organic carbon, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Cd, Cr, Ni, As and Pb), and biological (microbial contamination) properties.
In the second phase, growing media prepared using sewage sludge and potting mixture at different proportions were taken as treatments. Eleven treatments namely T1- potting mixture alone (soil, sand and FYM 1:1:1), T2- potting mixture + sewage sludge (9:1), T3- potting mixture + sewage sludge (8:2), T4- potting mixture + sewage sludge (7:3), T5- potting mixture + sewage sludge (6:4), T6- potting mixture + sewage sludge (1:1), T7- potting mixture + sewage sludge (4:6), T8- potting mixture + sewage sludge (3:7), T9- potting mixture + sewage sludge (2:8), T10- potting mixture + sewage sludge (1:9), and T11- sewage sludge alone were selected. Suitability of these growing media for ornamentals was evaluated in a pot culture experiment using marigold as test crop. The design adopted was CRD with three replications. The physical, chemical and biological properties of the growing media were analysed before and after the crop. The plant growth parameters (plant height, no. of primary branches, no. of secondary branches), yield and yield attributes (dry matter yield of shoot and root, flower yield) were recorded. The content and uptake of heavy metals in plant (shoot and root) were analysed.
The results revealed that the sewage sludge generated from Muttathara treatment plant was strongly acidic (pH 2.91). The organic carbon content was high (12.2%). It was rich in plant nutrients N (2.05%), P (2.65%), K (1.80%), Ca (1.02%), Mg (0.63%), S (460 mg kg-1), Fe (3.2%), Mn (0.15%), Zn (224.7 mg kg-1), Cu (225.5 mg kg-1) and B (13.5 mg kg-1). Physical properties namely water holding capacity (26.1%) and porosity (65.7%) were high. Bulk density was very low (0.65 g cc-1). The sludge contained the heavy metals Pb (11.5 mg kg-1), Cr (31.5 mg kg-1), Ni (33.5 mg kg-1) and Cd (27 mg kg-1). Presence of E.coli was also detected (> 2400 MPN/ 100g).
Analysis of physical, chemical and biological properties of growing media revealed that pH decreased with the increasing content of sewage sludge in media. T11 recorded the lowest pH (2.89) and the highest pH was noticed in T1 (6.23). There was a significant increase in the organic carbon content with increasing levels of sewage sludge in the growing media. The water holding capacity, porosity, content of major nutrients, secondary nutrients and micronutrients were also found to increase from T1 to T11. The content of heavy metals Cd, Cr, Ni and Pb increased from T1 to T11. Presence of E. coli was not detected in any of the treatments. The analysis of post-harvest growing medium also showed the same trend for all the parameters.
T2 recorded the maximum number of flowers (79.60 plant-1) and flower yield (706.36 g plant-1). It was also superior with respect to vegetative and floral parameters but was on par with T3. The heavy metal content in plant (shoot and root) was significantly influenced by treatments and the highest in T11. The treatments did not significantly influence chlorophyll in leaves and xanthophyll, flavonoid in flower.
Based on the results of the present investigation it can be concluded that the sewage sludge generated from sewage treatment plant Muttathara is rich in organic carbon and plant nutrients. However it is highly acidic and also contain heavy metals. Presence of heavy metals and microbial contamination are limiting
its direct use as a growth media. E. coli though detected in raw sewage sludge, was not present in the growing media prepared with the sludge. The pot culture experiment results indicated that the growth and yield of marigold was significantly higher in the treatment receiving potting mixture and sewage sludge in the ratio 9:1. The content of heavy metals (Cd, Cr, Ni, Pb) in shoot and root of marigold were found to be above the permissible limit in treatments containing sewage sludge indicating significant bioaccumulation of heavy metal from sewage sludge by marigold.