A study of olive mill wastewaters obtained from different treatment processes effects on chemical and microbial properties of a Typic Xerofluvent soil and wheat yield

Nur Okur,Delia Sponza Teresa,Bülent Okur,Bülent Yağmur,Recep Serdar Kara,Hüseyin Hüsnü Kayikçioğlu

doi:10.3906/tar-1902-75

Abstract

This study was carried out to investigate the potential for the usability of treated olive mill wastewater (OMW) as an organic amendment in agricultural soils under Mediterranean climate conditions. OMW was treated by two different treatment processes as economical (E-OMW) and advanced (A-OMW). The treated OMWs and raw OMW (R-OMW) were applied to a loamy soil at a rate of 100 m3 ha-1 year-1 for 2 years. Soils were sampled 15 days and about 5 months (at harvest) after OMW application for chemical and microbial analyses in each year. The total concentrations of N, P, Cu, Zn, and phenol of R-OMW decreased after both treatment processes while salinity (EC) and the total amounts of K, Na, and Ca increased. The applications of OMW caused changes in soil chemical (pH, EC, Pext, Kext) and microbial (microbial biomass-C (MB-C), microbial biomass-N (MB-N), basal soil respiration (BSR), N-mineralization (N-min)) characteristics (P < 0.05). In the second year of the experiment, initial samplings showed that the values of soil pH and EC increased significantly under all OMW applications compared to the control. High Pext concentrations were determined in soils amended with R-OMW, while there were high Kext concentrations in soils amended with the treated OMWs. The increases determined in MB-C and MB-N at all sampling times resulted in high MB-C/TOC and MB-N/TN ratios in soils amended with the treated OMWs. The wheat grain yield over the 2-year period showed that the application of the treated OMWs had a positive effect. It was determined that no negative effects occurred for either soil properties or wheat growth with the treated OMW applied at rates of up to 100 m3 ha-1. The addition of treated OMW after removal of its phenolic components may be considered as a good option for evaluating this waste in countries where OMW causes serious environmental pollution.

Highlights

The olive tree (Olea europaea L.) is one of the most important cultivated crops in Turkey, which gives the olive oil sector remarkable economic importance in West and Southwest Anatolia
The total concentrations of Mg, Fe, and Mn of R-olive mill wastewater (OMW) increased after the advanced treatment process while they decreased after the economical treatment process
The effect of the treated OMWs on microbiological properties of soil was more pronounced than the effect of raw OMW (R-OMW)

Summary

Introduction

The olive tree (Olea europaea L.) is one of the most important cultivated crops in Turkey, which gives the olive oil sector remarkable economic importance in West and Southwest Anatolia. About 178,000 t of olive oil is produced in Turkey, representing 5.8% of the world production (IOC, 2018). The countries producing olive oil have the problem of the disposal of the wastewater from olive mills where the olives are processed and oil is extracted (Erses Yay et al, 2012). The olive oil extraction process in Turkey annually generates about 923,000 m3 of olive mill wastewater (OMW) (Murat Hocaoğlu, 2015). One alternative and economical solution for OMW disposal is controlled land application (Erses Yay et al, 2012). In some Mediterranean countries, such as Italy, Portugal, and Spain, application rates of about 30 to 80 m3 ha–1 year–1 of OMW to agricultural lands are permitted (Sierra et al, 2007). In Turkey, there is no specific regulation or permitted rate regarding the

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