Svetla Marinova1, Martin Banov2, Rositsa Georgieva3, Daniela Stankova3, Ginka Paunova3, Vesela Georgieva3 and Yordan Tachev3
1 Institute of Soil Science, Agrotechnology and Plant Protection „Nikola Poushkarov“, 1000 Sofia, Bulgaria
2 Agricultural Academy, 3300 Sofia, Bulgaria
3 National Center for Public Health and Analysis, 1000 Sofia, Bulgaria
Marinova, S., Banov, M., Georgieva, R., Stankova, D., Paunova, G., Georgieva, V. & Tachev, Yo. (2023). Effect of using sludge from waste water treatment plants as an organic reserve in agriculture. Bulg. J. Agric. Sci., 29 (3), 417–429
Large amounts of sludge are produced in the biological treatment of wastewater. They accumulate in the areas off treatment plants and can pollute the natural environment. Many studies carried out to characterize the sludge found that they are biomass and represent an organic reserve in connection with the lack of organic fertilizers in our country and disturbed balance of organic matter in the Bulgarian soils. It is necessary to establish the effect of sludges as a fertilizer and their influence on the yield and quality of plant production and the soil. The results were compared with those obtained using the manure.
The purpose of the study is to determine the effect of using WWTP sludge and the impact on the yield and quality of plant production and soil. To compare with the effect of using manure.
A vegetation experiment was conducted on two soil types – leached cinnamon soil and smolnitza. Two soil improvers were used – sludge from WWTP and manure from a cow farm. An indicator crop is silage corn. Experiments were carried out at a percentage of sludge and manure (5%, 15%, 25%) by weight of the soil, including controls, without added improvers. 3 kg soil conteiners were used in 4 repetitions. The experiment was performed out in 2020. Standardized laboratory methods have been applied. When collecting the indicator crop, the yield was reported and a mathematical-statistical analysis was made. Maize was harvested, according to variants in the 7-8 leaf phase, being drawn from each pot -container separately, after which the results were averaged from the individual replicates. The plant production and the soil from the different variants were analyzed according to chemical, agrochemical and microbiological parameters. A comparison was made with the effect of using manure.
It was established that the sludge does not contain heavy metals above the MPC and other pollutants that may limit its use in agricultural practice. The yield of maize grown on smolnitza and cinnamon forest soil increases as the fertilization rate increases. Higher yields are obtained, when using the sludge on the cinnamon forest soil, while the smolnitza responds better to manure fertilization. The statistical analysis shows that the main factor influencing the yield is the rate of fertilization, followed by the type of improver applied and the soil difference. The results were compared with those obtained using the manure. No negative impact on plant production was observed when using the sludge. The sludge have a positive impact on the soils, as they are rich in macro- and microelements and the values of heavy metals are below the MPC indicated in the legislation. The sludge did not burden the two types of soils used in the vegetation experiments with faecal bacterial flora, both in terms of indicator microorganisms and pathogens.
The obtained results build on the conducted research and establish that sludge from WWTP is not inferior to organic fertilizers and can be used as an organic reserve, in connection with the shortage of organic sources in our country and disturbed balance of organic matter in Bulgarian soils, according to the requirements of the legislation.