Impact of Fresh and Fermented Palm Oil Mill Effluents on Soil Physicochemical Parameters and Enzyme Activities in Umuaka, Njaba, Imo State of Nigeria

Abstract

The impact of palm oil mill effluents (POME) on soil fertility was determined by studying the physico-chemical and heavy metals parameters found in fresh and fermented POME from six palm oil milling sites. Some soil enzymes (like catalase, dehydrogenase and lipase) and physico-chemical parameters of POME polluted soil wereevaluated from six dumpsites and soil from ten-yards distance from dumpsites in relation to the control farmland in the area. The fresh and fermented POME samples were randomly collected aseptically from small scale palm oil milling sites in Umuaka inNjaba Local Government Area ofImo State, Nigeria. The soil samples were collected aseptically into sterile containers from topsoil (0 – 15cm deep), and subsoil (15 – 30cm deep) at dumpsites, ten-yards distance from dumpsites and farmland one kilometre from various dumpsites. The study of both soil and POME samples were carried out using standard analytical procedures. The analysis of variance of the results of physicochemical parameters in POME samples showed that there were significant(p<0.05) differences in all the parameters which include: pH, magnesium ion (Mg2+), calcium (Ca2+), potassium (K+), sodium (Na+), total solid (TS), suspended solids (SS), total volatile solids (TVS), chemical oxygen demand (COD), dissolved oxygen (DO), nitrogen (N) and phosphorus (P) in fermentedPOME when compared tofresh POME.The concentration of heavy metals in the POME samples showed that they were rich in chromium, copper, iron and lacked cadmium. The results of the soil fertility parameters showed that POME polluted soils are rich in soil nutrients such as nitrogen, organic carbon (OC), organic matter (OM), cation exchange capacity (CEC) and most especially exchangeable cations (Mg2+, Ca2+, K+ and Na+) in topsoils and subsoils than in their respective non POME polluted soils. Although the results of the soil fertility analysis showed that POME-polluted soil had high fertility index, it has low phosphorus content which was due to negative effect of the acidic pH of the POME on phosphorus availability.The analysis of the results of activities of soil enzymes in the POME- polluted soil showed that discharge of the fresh and fermented POME caused induction of lipase activity. Catalase activitydecreasedsignificantly (p<0.05)from 1.35±0.02 to 0.33±0.01 mM H2O2/g soil/h for topsoil and 2.08±0.08 to 0.21±0.01mM H2O2/g dry soil/h for subsoil from dumpsites respectively while dehydrogenase activity in topsoil and subsoil ten yards away from dumpsitedecreasedsignificantly (p<0.05)from 1.35±0.02 to 0.18mM H2O2/g soil/h and 2.08±0.08 to 0.21±0.01mM H2O2/g dry soil/h,respectively. Dehydrogenase activitydecreasedsignificantly (p<0.05) from 0.76±0.001 to 0.10 mg/gdrysoil/96h for topsoil and 0.86±0.01 to 0.077±0.01mg formazan/gdrysoil/96h for subsoil from dumpsites while dehydrogenase activity in topsoil and subsoil ten yards away from dumpsitedecreasedsignificantly (p<0.05) from 0.76±0.001 to 0.10±0.03 mgformazan/gdrysoil/96h and 0.86±0.01 to 0.07±0.01 mgformazan/gdrysoil/96h, respectively. Furthermore, the results obtained for the soil pH indicate that the soils are acidic and have high exchangeable acidity. Considering the high fertility potentials of POME, it is necessary to make good effort to maximize these potentials by reducing its high pollution level such as BOD, COD, heavy metals, oil and grease in the fresh and fermented POME.