Co-composting of faecal sludge and organic solid waste for agriculture: process dynamics.

This paper presents the potentials and performance of combined treatment of faecal sludge (FS) and municipal solid waste (SW) through co-composting. The objectives were to investigate the appropriate SW type, SW/FS mixing ratio and the effect of turning frequency on compost maturity and quality. Solid waste (SW, as market waste, MW, or household waste, HW) was combined with dewatered FS in mixing ratios of 2:1 and 3:1 by volume and aerobically composted for 90 days. Four composting cycles were monitored and characterised to establish appropriate SW type and mixing ratio. Another set of five composting cycles were monitored to test two different turning frequencies: (i) once in 3-4 days during the thermophilic phase and 10 days during maturation phase and (ii) once in every 10 days throughout the composting period. Samples were taken at every turning and analysed for total solids (TS), total volatile solids (TVS), total organic carbon (TOC), electrical conductivity (EC), pH, ammonium and nitrate nitrogen (NH(4)-N and NO(3)-N) and total Kjeldahl nitrogen (TKN). Temperature, C/N ratio, NO(3)-N/NH(4)-N ratio and cress planting trials were chosen as maturity indicators. Result showed a preference of MW over HW and mixing ratio of 2:1 over 3:1. There was no significant effect of different turning frequencies on the temperature changes and the quality of mature compost. The final product contained C/N ratio of 13 and NO(3)/NH(4)-ratio of about 7.8, while TVS was about 21% TS and the NH(4)-N content was reduced to 0.01%. A co-composting duration of 12 weeks was indicated by the cress test to achieve a mature and stable product. The turning frequency of 10 days is recommended as it saves labour and still reaches safe compost with fairly high nutrient content.

S-metolachlor pulse exposure on the alga Scenedesmus vacuolatus: effects during exposure and the subsequent recovery.

In streams and creeks, the aquatic flora is exposed to fluctuating concentrations of herbicides during and following their application. Peak concentrations of herbicides, like the chloroacetanilide S-metolachlor, are usually detected following rain events. In this study, we assessed the effect of S-metolachlor pulse exposure on the algae Scenedesmus vacuolatus. We measured the time-dependency of effects during exposure on algae population and identified the algae development stage most sensitive to S-metolachlor. Furthermore, we assessed the time-to-recovery of the algae following exposure. A 6h pulse exposure at 598microgl(-1) was sufficient to inhibit cell reproduction by 50%. However, the exposure period had to coincide with the cell development stage specifically inhibited by S-metolachlor, which is the end of the cell growth phase. In algae populations composed of cells at all development stages, we initially observed an increase in the size of some algal cells, ultimately leading to an inhibition of the growth rate. In these experimental conditions, effects were observed after 18h of exposure and greatly increased with time. The recovery of algae following exposure to strongly inhibiting S-metolachlor concentrations was delayed and only occurred after 29h. These findings suggest that peak exposure to S-metolachlor may affect the growth of sensitive alga in surface waters, considering that the effects extend beyond the period of exposure.

Helminth eggs inactivation efficiency by faecal sludge dewatering and co-composting in tropical climates.

This study investigates helminth eggs removal and inactivation efficiency in a treatment process combining faecal sludge (FS) dewatering and subsequent co-composting with organic solid waste as a function of windrow turning frequency. Fresh public toilet sludge and septage mixed at a 1:2 ratio were dewatered on a drying bed. Biosolids with initial loads of 25-83 helminth eggs/g total solids (TS) were mixed with solid waste as bulking material for co-composting at a 1:2 volume ratio. Two replicate sets of compost heaps were mounted in parallel and turned at different frequencies during the active composting period: (i) once every 3 days and (ii) once every 10 days. Turning frequency had no effect on helminth eggs removal efficiency. In both setups, helminth eggs were reduced to <1 viable egg/g TS, thereby complying with the WHO guidelines 2006 for the safe reuse of FS.