Adv. Agric. Biol. 5 (2), 2016: 24-30 © PSCI Publications Advance in Agriculture and Biology www.pscipub.com/AAB E-ISSN: 2310-9343 / P-ISSN: 2311-0163 DOI: 10.15192/PSCP.AAB.2016.5.2.2430 Phytoassessment of a spent carbide-contaminated soil obtained from an auto mechanic workshop after substrate amendment with digestate obtained from a biogas plant in Benin City Ikhajiagbe B 1 , Mshelmbula BP 2 1. Environmental Biotechnology and Sustainability Research Group, Department of Plant Biology and Biotechnology, University of Benin, Nigeria 2. Department of Biological Sciences Adamawa State University, Mubi, Nigeria *Corresponding author email: barkapeter5@gmail.com Paper Information A B S T R A C T Received: 21 December, 2015 Accepted: 13 February, 2016 Published: 20 March, 2016 The study investigated the improvement in soil quality of soil collected from an auto mechanic workshop that had been polluted with spent carbide and spent engine oil waste (SEOW) after amendment with digestate from biofuel production. The remediated soil was later phytoassessed by using germination and growth parameters of Telfaria occidentalis (pumpkin) as yardstick. The physico-chemical properties, heavy metal content and total hydrocarbon content (THC) of the soil were also investigated. The soil was polluted with SEOW of 5%w/w and four different levels of spent calcium carbide treatment of 0%, 2.5%, 5.0%, and 10.0% w/w. One set was amended with digestate (+D) while the other set was unamended (ND). The result obtained showed that soil pH increased from 7.10 at the start of the experiment to 9.35 – 11.2 three months later when soil was subjected to experimental conditions. Also significantly increased were the soil’s electric conductivity from (420 to 680 μS/cm) and potassium content (0.51 – 1.09 meq/100g). There was significant reductions in all the heavy metals sampled 3 months after exposure to the experimental conditions. Higher concentrations of spent carbide in the soils implied lower remediation of heavy metals and total hydrocarbons. Phytoassessment with T. occidentalis shows that generally, the plant in 10% carbide amended-oil polluted soil (digestate amended) did not survive, whereas those ones in the non-amended soil (10 %C, ND) survived. Plant height in 10 %C (ND) was 48.8 cm and a yield of 33 leaves per plant, compared to the control (0 %C, ND) which height and number of leaves were 41.5 cm and 50 leaves respectively. There were no significant differences between plants parameters in polluted soils of similar carbide concentration irrespective of whether or not the soils were eventually substrate amended with digestate. © 2016PSCI Publisher All rights reserved. Key words: Phytoassessment, biofuel digestate, amendment, spent carbide, hydrocarbon, calcium carbide Introduction A major part of the natural ecosystem is the soil. Plants, animals, microorganisms and man rely on it for survival (Adriano et al., 1998). Plants require a pleasant environmental condition and nutrient to be provided for them to grow well. Unfortunately, unmanaged, over and ever increasing human population is beginning to occupy rich agriculture lands. Areas around towns and big cities, which were fertile and cultivated a decade ago, has replaced now by housing schemes and factory works, as well as oil-polluted soils partuiclularly as a result of indiscriminate dumping of waste lubricating oil. Some of these oil-polluted soils in most mechanic shops visited in Benin City, Nigeria, also complicate the oil-polluted soil situation by also dumping spent calcium carbide, which the auto mechanics use. A very popular practice by auto mechanics in Benin City is the siting of workshops on open vacant plots either very close to farmlands or, in vry many cases, on unused portions of farmlands. Compared with the past, today we have more mouths to feed and more bodies to dress but no more land for the cultivation of arable crops. This situation forces one to increase per unit area production of major crops like fluted pumpkin, which is about the most popularly sort after vegetable crop in the City. Vegetables are an important part of human’s diet. In addition to a potential source of important nutrients, vegetables constitute important functional food components by contributing protein, vitamins, iron and calcium which have marked health effects. Vegetables, especially those of leafy