An evaluation of the phytotoxicity of municipal solid waste during co-composting with different animal manures

Composting is a bioxidative process carried out under controlled conditions which utilizes naturally occurring microorganisms for organic waste recycling. In this study, a 60 days cocomposting experiment of different treatment consisting of municipal solid wastes and plant wastes with cow dung, poultry dropping and swine manure were investigated.Compost maturity parameters and phytotoxicity, during co-composting of municipal solid waste (MSW) with different animal manures (3:1 w/w) were evaluated. Four composting treatment set-ups: MSW (control), MSW+Swine Manure (SM), MSW+Poultry Manure (PM) and MSW+Cattle Manure (CM) were prepared and composting carried out for 60 days. Changes in temperature and pH were measured daily while Electrical Conductivity, Organic Matter, Total Organic Carbon, Total Kjedahl Nitrogen, and carbon/nitrogen ratios were assessed at day 0 and day 60. Humification process and phytotoxicity of the treatments were assessed at days 0, 10, 20, 30, 40, 50 and 60, using maize seeds germination bioassays. MSW+PM treatment showed the highest temperature of 63oC during the thermophilic phase while the control showed the least. The pH at the end of composting in all treatments exhibited alkaline values with MSW+CM showing the highest value of 8.6. Maturity indices showed that there were significant decreases in organic matter, C/N and NH + -N/NO -N ratios in all the treatments when compared with the control. At the end of 4 3 composting, Germination index( GI) values varied from 52.56 to 97.23% with MSW+PM showing the highest germination index (GI?) of 97.23±6.08% followed by MSW+CM and MSW+SM with GI values of 88.4±6.3 and 84.8±5.3% respectively. The germination index indicated that there were significant reductions in the phytotoxicity of the treatments.


Introduction
for densely populated cities in many developing Global concerns on the environment in countries. recent times have encouraged world leaders to put In Nigeria, the volume of municipal waste and in place legislative and regulatory measures aimed bio solids has ever been increasing, particularly in the at promoting sustainable development in many major cities and towns, owing ostensibly to increase in countries worldwide. One key feature of these population and by extension anthropogenic activities measures has been the greater emphasis on (Ogunwande et al., 2008). Presently, the main reducing waste volume through recycling as well as municipal solid waste (MSW) disposal method is a move away from solid waste landfilling (Cunha-through unsanitary landfilling and incineration at open Queda, 2007;Xiao et al., 2009). Solid waste dump sites. This practise produces much of secondary management through effective disposal methods pollutants, such as landfill leachate, greenhouse gases has become a considerable issue albeit a challenging and odour. task to the relevant government agencies especially Presumably, owing to the enormous investment, long processing cycle and unstable and subjected to analysis. products in a conventional composting treatment, only a few MSW are treated by composting in Physico-chemical analysis Nigeria. composting, whose chief aim is to convert The moisture and organic matter (OM) organic waste into a relatively stable material contents of the samples were determined after drying at reduces the volume and stabilizes the waste to 105°C for 24 h and ashing at 55°C for 4 h respectively obtain a final product that is stable, free of (Curtin et al., 2012). The pH and electrical conductivity pathogens and without phytotoxicity to plants (EC) were determined in aqueous extracts (1:10) using (Choy et al., 2015;Selim, 2012 In the evaluation of compost quality, a followed by analysis with the molybdate-ascorbate number of physico-chemical parameters such as method while the total organic carbon (TOC) was pH, electrical conductivity, carbon form, inorganic determined according to the colorimetry method as nitrogen forms and cation exchange capacity and described (Gabhane et al.,2012). The C/N ratio was biological parameters such as germination index computed from contents of Total Organic Carbon (TOC) have been used successfully as indicators of and total nitrogen in dried samples. The humic acid compost stability and maturity of different compost and fulvic acid concentrations were determined on the mixes. In this regard, one of the most widely test sample extracts using 0.1 M Na P O + NaOH 4 2 7 accepted parameter is the seed germination test extraction and precipitation at pH 2 followed by which is also a measure of the phytotoxicity spectrophotometric measurement at 465 and 665 nm (CunhaQueda et al., 2007).
respectively (Huang et al., 2015). Thus the purpose of this investigation is to comparatively evaluate some maturity indexes and Germination test phytotoxicity of municipal solid waste co-The seed germination tests were performed composted with different manures in a rotary drum with maize seeds (Zea mays) according to the method (composter) under 60 days, using the germination described by Selim et al.,, 2012. The test were carried tests of maize seeds (Zea mays).
out on the 10% crude aqueous extracts of the compost sample. A quantity (0.5 ml) of each extract was Materials and methods pipetted into a sterilized plastic petri dish lined with a Composting and sampling Whatman No 2 filter paper. Ten maize seeds were then The municipal solid waste (MSW) was evenly placed on the filter paper and incubated at 25°C collected from dump site in Ile-Ife, Osun state , in the dark for 72 hrs after which treatments were Nigeria. It was source selected before use. Fresh evaluated by counting the number of germinated seeds cow dung was obtained from the Adesanmi abattoir, and measuring the length of roots. Three replicates for Ede road, Ile-Ife while the poultry manure and each sample of the compost. The germination index swine manure were obtained from the respective (GI) was computed using the following formula: animal units at the Teaching and Research Farm of G.I = (Gt x Lt)/(Gc x Lc) x100 the Obafemi Awolowo University. The experimental Where: Gt =% of seed germination in test sample set-ups were made up of four composting Gc= % of seed germination in control treatment mixes consisting of thirty kilograms (30 Lt = root length in test sample kg) each of a mixture of the MSW and animal Lc = root length in control manures (3:1, w/w) as follows: (i) MSW (Tiqua , 2010;Selim et al., 2012) (Control) (ii) MSW + Poultry Manure (PM) (iii) MSW + cattle manure (CM) and MSW + Swine Statistical analysis manure (SM). Composting was carried out in a Data are expressed as means ± Standard error perforated rotary drum composter (H = 0.35m, D of the mean (SEM) of three independent sample = 0.30m) for 60 days and the drums were replicates. One way analysis of variance (ANOVA) was rotated once every 3 days. Moisture content was performed to compare the means of treatment set-ups. maintained to 60 -65% during composting.
Difference between means were statistically analysed Triplicate compost samples were collected from the using a software package, GraphPad® Instat (version rotary drum, air-dried, ground to below 0.25 mm 1.4). The least significant difference test at p=0.05 was carried out to compare means. (Ko et al,.2008). It has been reported that an excessive duration of thermophilic phase (beyond 6 weeks) as Results and Discussion observed in the MSW (control) treatment may indicate The four composting treatment set-ups an abnormally extended decomposition and a delayed achieved thermophilic temperatures (>45°C) after transition to the stabilization stage (Satisha and 10 days (Fig. 1). These temperatures were Devarajan, 2007). maintained for 15-25 days, and gradually declined The pH values observed were in the range to ambient values thereafter. The thermophilic between 6.3 and 8.6 (Fig. 2). The lowest pH values phase lasted for 10 days longer in MSW control than (6.3) at the start of composting was observed in the in the other treatment set ups. The duration of high MSW + SM treatment while the highest 8.6 was temperatures is consistent with results from similar observed in MSW + PM. No consistent pH trend was studies, and has been reported to reflect the usually observed for all the treatment set ups throughout the high proportion of degradable substances that are duration of the composting experiment, however, the found in this type of waste (Tognetti et al., 2008, pH values in all treatments increased to the alkaline Curtin et al., Sundberg et al., 2013 ( Tognetti et al., 2008). Values represent mean ± SEM, n=3, * significantly different from MSW (Ctrl), (p < 0.05)

Table 1. Physicochemical parameters at the initial and final stages composting of municipal solid waste with different animal manures
Each data represent mean ± SEM, n=3, * significantly different from final MSW (Ctrl), † significantly different from initial value. (p<0.05)

Figure 4. Changes in % humic acid during the composting of municipal solid waste with different animal manures
Values represent mean ± SEM, n=3, * significantly different from MSW (Ctrl),(p < 0.05)

Figure 5: Changes in germination index during the composting of municipal solid waste with different animal manures
Values represent mean ± SEM, n=3, * significantly different from MSW (Ctrl), (p < 0.05) Other studies have attributed alkaline the control (Table 1). A sharp increase in EC values due values of municipal organic waste composts to the to the release of soluble salts like ammonium and presence of wood ashes in the wastes (Tognetti et phosphate after the degradation of the most labile al., 2008), which could be a common occurrence in compounds in the thermophilic stage of composting has the area from where the MSW samples used in this been reported by several investigators (Tiquia 2010 ). It is study was obtained, being a semi urban city. Kong, well established, that EC reflects the salinity of an D. et al., (2012) had earlier noted that the change organic amendment and that high salt concentration of mesophilic to thermophilic conditions during has been reported to cause phytotoxicity problems and municipal waste composting coincided with a therefore EC is a good indicator of the suitability and change in pH from acidic (<6) to alkaline (8-9). safety of compost for agricultural purposes (Tiquia These alkaline values were attributed to proton 2010). Since none of the treatment set-up had EC value -1 consumption during decomposition of volatile fatty exceeding the threshold value of 4 dS m it may acids, which is usually abundant in the initial indicate that the compost samples can be safely applied mesophilic phase, during which organic-N to soil (Ko et al ., 2010). mineralization to NH + -N occurs as a result of With respect to the maturity and stability 4 parameters measured, the results showed that at the intensive proteolysis during protein degradation end of the composting period most of the observed (Satisha and Devarajan, 2007).
values had attained thresholds as recommended by In the present study, MSW + PM had the different investigators (Table1). For instance, in all the highest pH values, possibly due to intensive treatments except for the MSW (Ctrl) the OM <10 thermophilic phase, which could have favoured mg/kg, C/N < 20, NH + -N < 400 mg/kg, NO --N > extensive organic-N ammonification when  Selim et al., 2012) . In case of ( Barenna et al., 2008;Antil, 2014)., to be indicative of MSW control the salt concentration might have inhibited active mineralization of OM by microorganisms.
the maize development. This observation apparently indicates all the three manures stock are suitable for composting of Conclusion municipal organic waste and that maturity of It can be inferred from this study that the compost could be achieved within a 60 days period maturity parameters and germination index of the when carried out under controlled composting different compost indicates that though all the three conditions as employed in this study such as the use animal manures could be used as suitable activators for of a rotary drum.
the composting of municipal solid waste, poultry As shown in Fig. 4, the concentration of manure had the best activating properties amongst the humic acid as a percentage of humic substance three manures under the experimental conditions used increased gradually over the first 20 days and then in this study. These observations could be relevant for increased sharply from 25 to 60 days in all the the improvement of municipal solid waste management treatment groups except in MSW (ctrl). MSW + PM in many developing economies. Furthermore the low and MSW + CM showed quite a remarkable and technical and economical requirements of the modified significant (p < 0.05) increases compared to MSW Rapid Berkly method as used in this study could make it + SM . By contrast, the concentration of fulvic acid a promising option in unban localities. which is a relative seed and eucalyptus bark. Biores. Techn. 98: 3213-3220. germination ratio to that of root growth is an indicator of phytotoxicity and one of the veritable Fialho, L.L., Lopez da Silva, W.T., Milori, D.M.B., Simoes, M.L., index in assessing compost maturity and stability Martin-Neto, L. (2010). Characterization of organic matter (Selim et al., 2012). It is generally considered that from composting of different residues by physicochemical and phytotoxicity is eliminated when GI attains a level spectroscopic methods. Biores. Techn. 101(6) : 1927-1934 greater than 80% (Tiquia, 2010). In this maize seeds germination was inhibited by to a greater Gabhane, J., Williams S.P.M.P, Bidyadhar,P. Bhilawe, P., degree in the control set-up ie MSW control relative Anad, D., Vaidya, A.N and Wate, S.R. (2012). Addictives to the set ups. Generally germination index of aided composting of green wastes: Effects on organic values below 50% suggest that that phytotoxic matter decomposition, compost maturity and quality of compounds might have been fully metabolised thus