Co-composting of sewage sludge and Echinochloa pyramidalis (Lam.) Hitchc. & Chase plant material from a constructed wetland system treating domestic wastewater in Cameroon

Trials were conducted at the Cité-Verte domestic wastewater treatment station (Yaoundé-Cameroon) in order to assess the effect of three sewage sludge: Macrophyte ratios on the co-composting process and compost quality. The ratios were T1: 25 kg of plant material (Echinochloa pyramidalis) and 75 kg sludge; T2: 50 kg of plant material and 50 kg sludge, and T3: 75 kg of plant material and 25 kg of sludge. The assessment parameters of the co-composting process included the daily evolution of temperature, the pH and water content for each month. The quality of the mature compost obtained was analysed based on their C/N ratio, Ca, Mg, P, K, trace elements and helminth eggs content. During cocomposting, maximum temperatures ranged from 45.3 ± 4.7°C (T1) to 70.77 ± 2.76°C (T3). Mature cocompost was obtained after 3 months (T1), 4 months (T2) and 5 months (T3). Mean pH and C/N ratio of co-composts respectively ranged from 7.26 to 7.62 and from 10 to 15. In mature compost, the average values of organic matter, N and P respectively were 3323 ± 405 mg/kg, 165 ± 32 mg/kg and 36 ± 5 mg/kg for T1; 2945 ± 128 mg/kg, 152 ± 30 mg/kg and 27 ± 6 mg/kg for T2; and 228 ± 103 mg/kg, 105 ± 48 mg/kg and 7 ± 1 mg/kg for T3. K content was 1 mg/kg in all three co-composts. Heavy metals were found at trace levels. Helminth eggs concentration in compost was 0.2 ± 0.03 egg/g (T1), 0.1 ± 0.02 egg/g (T2) and 0.007 ± 0.01 egg/g (T3). All these co-composts did not present a significant hygienic risk with regards to WHO guidelines (2006) for safe reuse of faecal matter or faecal sewage in agriculture (less than 1 egg/g TS). For a given amount of plant harvested, it was concluded that the quickest way to produce a compost safe of parasites will be to mix them with 3/4 of sludge from the digestion tank.Key words: Co-composting, Cameroon, compost quality, Echinochloa pyramidalis, hygienic risk, sewage sludge

An effective organic waste recycling through vermicomposting technology for sustainable agriculture in tropics

peer reviewedPurpose The management of household wastes has been a real challenge for the capital city of Cameroon for some years now. In order to adopt ecological and sustainable strategies for better management of organic fraction of solid wastes, the present work was aimed to propose a sustainable alternative for the recycling of household organic waste through a vermicomposting process. Method A vermicomposting of household organic waste was carried out during 46 days, preceded by 23 days of pre-composting. Then, three treatments were established by mixing epigeic earthworms with different proportion of pre-composted waste. Maturation parameters such as pH, electrical conductivity (EC), C/N ratio, ammonium (N-NH4+ ) and total organic matter (TOM) were monitored about four weeks. The agronomic quality of the vermicompost was also determined at the end. Results During pre-composting, the temperature reached a maximum of 54.3±5.4°C suitable for the elimination of potential pathogen. The pH varied between 9.44 and 8.53 leading towards neutrality at the end of the vermi-composting process. The obtained mean values of C/N ratio and the TOM were respectively 11.04-11.68 and 25.82-27.19% in line with the AFNOR (NFU 44-051) guideline. The obtained vermicompost revealed high levels of nutrients such as N, P, K, Ca and Mg. The phytotoxicity test on lettuce showed germination rates above 50%, revealing the non-toxic nature of the vermicompost produced. Conclusion The vermicompost were rich in nutrients and exhibited the non-phytotoxicity. Thus, vermicomposting can be applied in the context of Cameroon to transform organic waste into organic fertiliser suitable for sustainable agriculture