Treatment technology for leachate from faecal sludge drying beds

The use of planted drying beds for faecal sludge treatment is effective for solid-liquid separation, but the leachate produced requires further treatment prior to discharge or reuse. This study investigates the potential of a new and low-cost solution for leachate treatment

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

Mosquito development in a macrophyte-based wastewater treatment plant in Cameroon

Abstract Macrophyte-based wastewater treatment systems are recognized as an alternative for sewage purification in developing countries. Unfortunately, they also represent a favorable breeding ground for mosquitoes, thus a serious drawback that should be addressed despite the good promise of this technology. A 1-year study of mosquito production in seven ponds of a Pistia stratiotes-based domestic wastewater treatment plant in Cameroon revealed that approximately 43 imagoes/m 2 per day rose up, among which 54% were female. Mansonia and Culex were the main breeding genera with about 55 and 42% of the total imagoes respectively. Culex bred mostly in the first three ponds (B1-3), characterized by a high organic pollution. Mansonia occurred in great number in the later ponds (B4-7), where the water quality was rather better and the roots of P. stratiotes well developed, thus permitting the fixation of a great number of larvae to the macrophyte roots. Though representing a favorable breeding ground for mosquitoes, only 0.02% of captured imagoes were Anopheles gambiae, suggesting that this wastewater treatment plant does not significantly contribute to the development of the malaria vector in this area

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

Modelling PAHs Transfer from Polluted Soil to Herbaceous Species in Phytoremediation Attempts

To address the soil–plant transfer modelling of 13 US-EPA Polycyclic Aromatic Hydrocarbons (PAHs), a mechanistic model—MM_19—has been developed based on the fugacity concept. For that, the Mackay_97 model has been improved in terms of reconsidering the losses related to the transport and transformation mechanisms taking place in the compartments—roots and aboveground shoots—of the three short-life species (Eleusine indica, Cynodon dactylon and Alternanthera sessilis). Model input parameters consist of both experimental and literature data, including the initial soil and air PAHs content, flowrates, PAHs physico-chemical properties, retention times and transport half-lives of PAHs inside plant species. Using in situ weather data and Penman’s law, xylem flows were estimated as the evapotranspiration for each plant. Model calibration was performed using a Generalized Reduced Gradient (GRG) nonlinear optimization solver method. Sensitivity analysis showed that the phloem flow was the most sensitive among all tested parameters. According to the Nash–Sutcliffe efficiency (NSE), the MM_19 model is more efficient than the Mackay_97 model for all three plant species. Finally, the impact of PAHs physico-chemical parameters on their sol-plant transfer was discussed in terms of slight, intermediate and high molecules weight. The NSE values showed that the MM_19 model is more efficient than the Mackay_97 model. Indeed, comparisons between experimental and simulated results in the MM_19 model showed similarities for each compartment of the plant species. Thus, the MM_19 model can be used to predict the soil–plant transfer of organic pollutants

Phytoremédiation de sols pollués par les hydrocarbures – évaluation des potentialités de six espèces végétales tropicales

Les écoulements et les transferts de matières à travers les sols et sous-sols sont des processus qui impactent les ressources en eau. Ainsi, la restauration des milieux dégradés participe à la préservation de la qualité de la ressource. Afin de contribuer à la décontamination des sols pollués par phytoremédiation - technique de dépollution basée sur l’action des plantes en association avec les micro-organismes du sol - des inventaires floristiques de sites potentiellement pollués et non pollués (témoins) par les hydrocarbures ont été réalisés dans quatre villes du Cameroun. Sur la base d'indicateurs floristiques, six espèces ont été sélectionnées, et leurs capacités phytoremédiatrices testées dans un sol pollué par du fioul à 82,5 mL∙kg‑1 de sol pendant 150 jours en présence de trois modalités : Tn - sols non pollués plantés (6), To - sols pollués non plantés (3) et Tp - sols pollués plantés (18). La biodiversité des sites pollués (106 espèces, 76 genres et 30 familles) est moins élevée que celle des témoins (166 espèces, 125 genres et 50 familles). Les espèces les plus fréquentes (Fri > 10 %) et abondantes (7 % < A < 10 %) sur les sites potentiellement pollués sont dominées par 15 espèces tropicales; parmi lesquelles, Eleusine indica (L.) Gaertn., Cynodon dactylon (L.) Pers., Alternanthera sessilis (L.) R. Br. ex DC†, Commelinpa benghalensis L., Cleome ciliata Schum. et Thonn., et Asystasia gangetica (L.) T. Anderson, sont utilisées dans des essais de phytoremédiation des sols contaminés au fioul domestique. Seules trois de ces espèces, notamment E. indica, C. dactylon et A. sessilis ont pu survivre et se développer. Contrairement à A. sessilis, E. indica et C. dactylon ne présentent pas de différence significative pour les paramètres de croissance considérés entre les modalités Tn et Tp. Les espèces E. indica et C. dactylon seraient donc plus tolérantes au fioul domestique que l’espèce A. sessilis.Flows and transfers of materials through soils and subsoils are processes that impact water resources. Thus the restoration of degraded areas contributes to the preservation of the quality of the resource. In order to contribute to the decontamination of polluted soil, phytoremediation (a clean-up technique based on the action of plants in association with soil microorganisms), floristic surveys of potentially polluted and unpolluted (control) sites by hydrocarbons were carried out in four cities of Cameroon. On the basis of floristic indicators, six species were selected and their phytoremediation capacities tested in a soil polluted by fuel oil at 82.5 mL∙kg‑1 of soil for 150 d in the presence of three modalities: Tn - unpolluted soil planted (6), To - unplanted polluted soils (3) and Tp - polluted soil planted (18). The biodiversity of polluted sites (106 species, 76 genera and 30 families) was lower than the controls (166 species, 125 genera and 50 families). The most frequent species (Fri > 10%) and most abundant (7% < A < 10%) on potentially polluted sites were dominated by 15 tropical species; among these, Eleusine indica (L.) Gaertn., Cynodon dactylon (L.) Pers., Alternanthera sessilis (L.) R. Br. ex DC†, Commelinpa benghalensis L., Cleome ciliata Schum. & Thonn. and Asystasia gangetica (L.) T. Anderson were used in phytoremediation trials on soil polluted with domestic oil. Only three of these species, including E. indica, C. dactylon and A. sessilis, were able to survive and develop. Unlike A. sessilis, E. indica and C. dactylon showed no significant difference for the growth parameters considered between the Tn and Tp modalities. E. indica and C. dactylon are therefore more tolerant to domestic oil than A. sessilis

Phytoremédiation de sols pollués par les hydrocarbures – évaluation des potentialités de six espèces végétales tropicales

Les écoulements et les transferts de matières à travers les sols et sous-sols sont des processus qui impactent les ressources en eau. Ainsi, la restauration des milieux dégradés participe à la préservation de la qualité de la ressource. Afin de contribuer à la décontamination des sols pollués par phytoremédiation - technique de dépollution basée sur l’action des plantes en association avec les micro-organismes du sol - des inventaires floristiques de sites potentiellement pollués et non pollués (témoins) par les hydrocarbures ont été réalisés dans quatre villes du Cameroun. Sur la base d'indicateurs floristiques, six espèces ont été sélectionnées, et leurs capacités phytoremédiatrices testées dans un sol pollué par du fioul à 82,5 mL∙kg‑1 de sol pendant 150 jours en présence de trois modalités : Tn - sols non pollués plantés (6), To - sols pollués non plantés (3) et Tp - sols pollués plantés (18). La biodiversité des sites pollués (106 espèces, 76 genres et 30 familles) est moins élevée que celle des témoins (166 espèces, 125 genres et 50 familles). Les espèces les plus fréquentes (Fri > 10 %) et abondantes (7 % < A < 10 %) sur les sites potentiellement pollués sont dominées par 15 espèces tropicales; parmi lesquelles, Eleusine indica (L.) Gaertn., Cynodon dactylon (L.) Pers., Alternanthera sessilis (L.) R. Br. ex DC†, Commelinpa benghalensis L., Cleome ciliata Schum. et Thonn., et Asystasia gangetica (L.) T. Anderson, sont utilisées dans des essais de phytoremédiation des sols contaminés au fioul domestique. Seules trois de ces espèces, notamment E. indica, C. dactylon et A. sessilis ont pu survivre et se développer. Contrairement à A. sessilis, E. indica et C. dactylon ne présentent pas de différence significative pour les paramètres de croissance considérés entre les modalités Tn et Tp. Les espèces E. indica et C. dactylon seraient donc plus tolérantes au fioul domestique que l’espèce A. sessilis.Flows and transfers of materials through soils and subsoils are processes that impact water resources. Thus the restoration of degraded areas contributes to the preservation of the quality of the resource. In order to contribute to the decontamination of polluted soil, phytoremediation (a clean-up technique based on the action of plants in association with soil microorganisms), floristic surveys of potentially polluted and unpolluted (control) sites by hydrocarbons were carried out in four cities of Cameroon. On the basis of floristic indicators, six species were selected and their phytoremediation capacities tested in a soil polluted by fuel oil at 82.5 mL∙kg‑1 of soil for 150 d in the presence of three modalities: Tn - unpolluted soil planted (6), To - unplanted polluted soils (3) and Tp - polluted soil planted (18). The biodiversity of polluted sites (106 species, 76 genera and 30 families) was lower than the controls (166 species, 125 genera and 50 families). The most frequent species (Fri > 10%) and most abundant (7% < A < 10%) on potentially polluted sites were dominated by 15 tropical species; among these, Eleusine indica (L.) Gaertn., Cynodon dactylon (L.) Pers., Alternanthera sessilis (L.) R. Br. ex DC†, Commelinpa benghalensis L., Cleome ciliata Schum. & Thonn. and Asystasia gangetica (L.) T. Anderson were used in phytoremediation trials on soil polluted with domestic oil. Only three of these species, including E. indica, C. dactylon and A. sessilis, were able to survive and develop. Unlike A. sessilis, E. indica and C. dactylon showed no significant difference for the growth parameters considered between the Tn and Tp modalities. E. indica and C. dactylon are therefore more tolerant to domestic oil than A. sessilis