Volatilisation of substances after spreading olive oil waste water on the soil in a Mediterranean environment

Abstract

The use of waste water in agriculture is widespread and its impact on the environment and human health needs to be investigated. The olive oil extraction process in Mediterranean countries produces large quantities of solid and liquid waste. Despite the fact that the liquid olive mill waste (OMW) contains a large number of pollutant substances, it is spread on the soil for agricultural purposes. In this paper, we present the results of the measurement of the emission into the atmosphere of volatile substances contained in olive oil waste water, after having spread it on the soil, in a site in southern Italy (Monopoli, Bari), during the years 2000 and 2001. The study was divided into three phases: (1) a preliminary test to screen the possible measurable volatile substances contained in the OMW; (2) a first trial in which the waste was spread in the morning; and (3) a second trial in which the waste was spread in the afternoon. In the preliminary test, only phenols, sulphur dioxide and hydrogen sulphide were found to be measurable. A micrometeorological method was used to measure the fluxes of these substances. This method involves the measurement, by means of gas tube detectors, of the concentration of gas at two levels, and the measurement of wind speed and air temperature at the same levels above the soil. Only phenols and sulphur dioxide were found to be detectable with the measurement method adopted, hydrogen sulphide was detected only in trace. In particular, when the OMW was spread on bare soil during the morning, 64.8±19.4 g ha −1 of phenols and 33.3±6.0 g ha −1 of SO 2 were emitted into the atmosphere over 5 days. When OMW was spread in the afternoon 37.5±11.2 g ha −1 and 34.8±6.6 g ha −1 of phenols and sulphur dioxide were emitted over 5 days, respectively, with a decrease of about 42% in the case of phenols. Therefore, this study showed that, to limit the noxious effects of the phenols on human health, the OMW should be spread in the second part of the day (afternoon).