Recycling of organic wastes through composting for land applications: a Nigerian experience.

In-vessel composting, a contribution to sustainable solid waste management, was conducted on source-separated waste materials generated in Abeokuta city, south-west Nigeria. Feedstock (household, agricultural and municipal waste) and the resultant composts were chemically characterized using standard procedures. Identification and changes in the microbial population during composting, the effects of composting on waste volume reduction (WVR) and elemental composition of composts were evaluated. Product performance on plant growth and metal uptake were then assessed using African spinach (Amaranthus hybridus) in a screen house for 8 weeks. Metals were determined in acid digest using atomic absorption spectrometry. Compost yields and WVR ranged from 35.28 to 48.68% and 51.66 to 64.72%, respectively. Compost heavy metal (Cu, Cr, Zn, Ni, Cd and Pb) concentrations (mg kg( -1)), ranging from 0.67-0.82; 0.13-7.5; 0.001-0.22; 1.67-18.33; 6.50-17.67; and 0.83-6.00 for Cu, Pb, Cd, Ni, Cr and Zn, respectively, were within limits for class A+ composts. The effect of composting varied with element type and significantly (p < 0.05) reduced microbial population by 44.44 to 88.46%. Plant height, leaf number and biomass yield gave positive correlations (r = 0.950 to 0.977; 0.978 to 0.989 and 0.99, respectively; p < 0.05) with applied compost rate. Low-metal composts were produced but the presence of Cd and Pb in plant tissues calls for further research on the long-term effect of products on plant metal uptake in amended soils. The study is a contribution to the data bank of composting as a low technology waste management option in the developing countries.

Assessment of blood and urine lead levels of some pregnant women residing in Lagos, Nigeria.

Assessment of lead in blood (BLL) and lead in urine (ULL) of some non-occupationally exposed, nonsmoking 214 pregnant Nigerian women, aged 17 to 49 years, and resident in Lagos was carried out using atomic absorption spectrometry with control subjects consisting of 113 nonpregnant women. From results, the mean BLL and ULL (µg/dL) for pregnant women (59.5±2.1; 29.4±1.1) were significantly (p<0.01) higher than the values obtained for nonpregnant women (27.7±1.1; 9.2±0.6). BLL found in women in the first, second, and third trimesters were 57.2±2.3, 61.6±2.2, and 63.1±1.8, respectively. ULL could not serve to predict BLL due to weak correlations (r=-0.06 to +0.15; p>0.10). Study is a contribution to blood and urine lead status of Nigerian pregnant women, being relevant for healthcare management purposes, public health decision making, and possible primary prevention activities.

Temperature effect on water extractability of cadmium, copper, lead and zinc from composted organic solid wastes of south-west Nigeria.

The effect of temperature changes (10 to 80 degrees C) on water-extractable metal (Zn, Cu, Cd and Pb) concentrations of composted wastes of Nigerian origin was investigated in batch extraction experiments. Metal concentrations were measured using a calibrated atomic absorption spectrophometer after acid digestions. Results showed that the water-extractable metal fractions (I) did not exceed 10% of total metal concentrations of the bulk composts, which corresponded to 0.30 to 6.63% for Zn, 0.09 to 7.51% for Pb, 1.83 to 9.29% for Cu and 0.67 to 9.23% for Cd. Water extractable metal fraction showed positive correlations (r = 0.137 to 0.917*; p* < 0.01) for Cu, Cd and Pb in most cases but negative for Zn (-0.067 to -0.445). Simulations revealed that a steady temperature rise from 0.1 to 1.5 degrees C might increase I by 0.13 to 168% for all the metals, although stability to gradual temperature rise was demonstrated in some instances. The study revealed that the degree of temperature effect on water extractability of heavy metals from the bulk composts was dependent on metal type, compost formulation and waste type.