Physicochemical and microbiological characterization of human faeces and urine from composting toilets in Abidjan, Côte d'Ivoire.

We assessed the physicochemical and microbiological properties of composting toilet products in Abidjan for their potential use in agriculture. Samples of urine and faeces were collected and analysed after 123 days of storage in plastic cans (urine) and 8 months of storage in closed composting bags (faeces). Selected physicochemical parameters (ammonium, phosphorus, potassium, calcium, magnesium) and pathogens (bacteria and helminths eggs) were monitored. Results showed that temperature and pH values were 26.0°C and 7.2, and 27.6°C and 8.6 for the faeces and urine, respectively. The physicochemical analysis revealed high nutrient contents and low trace metal levels in the faeces-based compost. Concentrations of magnesium, cadmium, copper, lead and zinc ranged from 0.46 to 54.98 mg/kg; while those of phosphorus, potassium and calcium were >700 mg/kg on average. In urine, the concentrations of phosphorus, potassium, calcium, copper and zinc were 930, 1240, 1402.8, 0.0672 and 0.121 mg/L, respectively. Various bacteria (including total coliforms, faecal coliforms, faecal streptococci and anaerobic sulphite reducers), along with Ascaris lombricoïds (1.66 eggs/g), were found in the faeces-based compost. Our findings indicate that the faeces-based compost was not homogeneous, namely with regard to the microbiological parameters, and additional time would be necessary to bring it to stability.

Effect of hydroxyapatite, octacalcium phosphate and calcium phosphate on the auto-flocculation of the microalgae in a high-rate algal pond.

Recovering microalgae is one of the main technological and economic concerns in a high-rate algal pond (HRAP) because of their small size and their low density. This paper emphasizes the characterization (identification and assessment of potential flocculation) of chemical compounds involved in microalgae auto-flocculation in a HRAP. First, thermodynamic simulations were performed, using two models (i.e. Visual Minteq and a simplified thermodynamic model) in order to determine the chemical compounds of interest. Experimental tests were then carried out with these compounds for assessing their flocculation ability. Both models revealed that precipitates of calcium phosphates and their substituted forms were the compounds involved in the auto-flocculation. Moreover, experimental tests showed that the stoichiometric neutralization of algal charges by calcium phosphates (i.e. hydroxyapatite (Ca5(PO4)3OH), octacalcium phosphate (Ca4H(PO4)3) and amorphous calcium phosphate (Ca3(PO4)2)), at a pH within the range 7-10 yields 70-82% recovered algal biomass. The optimum ratio required for algae auto-flocculation was 0.33 Ca5(PO4)3OH/g DM(algae) at pH 10, 0.11 Ca4H(PO4)3/g DM(algae) at pH 7 and 0.23 g Ca3(PO4)2/g DM(algae) at pH 9. Auto-flocculation appears as a simple, sustainable and promising method for efficient harvesting of microalgae in a HRAP.

A model for anaerobic ponds combining settling and biological processes.

This work presents an approach to an anaerobic pond model by combining the stoichiometry of the hydrolysis and acidogenic processes of the main constituents of wastewater, i.e. carbohydrates, proteins, and lipids, grouped as a 'combined substrate' with a previously published settling model (see 'Suspended solids settling and half removal time in stabilization ponds (Tunisia)' by Effebi et al. (2011)). This approach includes biomass production. Coupling the kinetics and stoichiometry of the previous processes with the usual methanogenic model, we developed an anaerobic pond model. This paper gives the stoichiometry of the different chemical reactions that occur during the degradation of a conventional influent (corresponding to what we define as a 'combined substrate') of domestic wastewater and the model's first results.