Hydraulic behaviour of vertical-flow constructed wetland under different operating conditions.

Five vertical-flow constructed wetland (VFCW) units planted with cattail (Typha augustifolia) were used to study the effects of feeding (continuous and batch), hydraulic loading rates (HLR) and drainage patterns (free drainage and percolate impounding) on hydraulic behaviour. The tracer studies were divided into two parts: (i) continuous feeding at an HLR of 0.005, 0.025, 0.05, 0.075, 0.1 and 0.3 m3 m(-2) d(-1) operating at different drainage patterns (i.e. free drainage and percolate impounding) and (ii) batch feeding at different water levels of percolate impounding (20, 30 and 40 cm). The results revealed that although the hydraulic behaviour of VFCW systems was strongly dependent on the operating pattern (feeding and drainage), it was not significantly affected by the hydraulic loading rate. The results of continuous feeding study concluded that (a) percolate impounding achieved an increase in HRT that was 1.6 times the HRT with free drainage, (b) the dispersion in both drainage patterns were moderate, and (c) the results from the tank-in-series (TIS) model correlated more closely with the data observed than with the dispersion plug flow (DPF) model. For batch feeding and percolate impounding, a uniform flow distribution of the tracer occurred in the water column after 2.1, 3.1 and 4.4 days for 20, 30 and 40 cm, respectively.

Improving environmental sanitation, health, and well-being: a conceptual framework for integral interventions.

We introduce a conceptual framework for improving health and environmental sanitation in urban and peri-urban areas using an approach combining health, ecological, and socioeconomic and cultural assessments. The framework takes into account the three main components: i) health status, ii) physical environment, and iii) socioeconomic and cultural environment. Information on each of these three components can be obtained by using standard disciplinary methods and an innovative combination of these methods. In this way, analyses lead to extended characterization of health, ecological, and social risks while allowing the comprehensive identification of critical control points (CCPs) in relation to biomedical, epidemiological, ecological, and socioeconomic and cultural factors. The proposed concept complements the conventional CCP approach by including an actor perspective that considers vulnerability to risk and patterns of resilience. Interventions deriving from the comprehensive analysis consider biomedical, engineering, and social science perspectives, or a combination of them. By this way, the proposed framework jointly addresses health and environmental sanitation improvements, and recovery and reuse of natural resources. Moreover, interventions encompass not only technical solutions but also behavioral, social, and institutional changes which are derived from the identified resilience patterns. The interventions are assessed with regards to their potential to eliminate or reduce specific risk factors and vulnerability, enhance health status, and assure equity. The framework is conceptualized and validated for the context of urban and peri-urban settings in developing countries focusing on waste, such as excreta, wastewater, and solid waste, their influence on food quality, and their related pathogens, nutrients, and chemical pollutants.

Recovery of biosolids from constructed wetlands used for faecal sludge dewatering in tropical regions.

Biosolids recovered from yard-scale vertical-flow constructed wetlands used for faecal sludge dewatering in Cameroon, were analyzed to assess their degree of maturity, nutrient and heavy metals contents, as well as their hygienic quality. Six beds were loaded weekly at nominal loading rate of 100, 200, and 300 kg TS/m2/year. The quality of the biosolids accumulated in the beds was monitored during 6 additional months of resting period prior to final harvest. Results showed that C/N ratio (11.3), humification index (14%), humification rate (1.8%), and degree of polymerization (3.7) of the biosolids generated were comparable to those of mature composts. Biosolids quality appeared to having high fertilizing value (N: 2%, P2O5: 2.3%, CaO: 1%, MgO: 0.14%, K2O: 0.03, and Na2O: 0.09%) with low heavy metals contamination (63, 14, 26, 2.4, 575, 703, 186, and 32 mg/kg for Pb, Ni, Cr, Cd, Cu, Zn, Mn, and Se, respectively). The concentration of fertile ascaris was reduced from 40 eggs/g TS after one month storage to <4 eggs/g TS after six month of storage, a level which does not significantly increase health risk exposure as compare to the WHO guidelines.

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.

Influence of sand layer depth and percolate impounding regime on nitrogen transformation in vertical-flow constructed wetlands treating faecal sludge.

Four laboratory-scale units of vertical-flow constructed wetlands (VFCW) were fed once a week with faecal sludge (FS) at a constant solids loading rate (SLR) of 250 kg TS/(m2.year) (equivalent to 260-300 gN/(m2.week)) for a period of 12 weeks to study: i) the nitrification and denitrification potential of the sand layer of VFCWs and ii) the effect of percolate impounding regime (permanent or batch-impounding) on nitrogen transformation. The TN content of raw FS was characterised by 65% org-N, 34% NH4-N and 1% NOx-N. After FS application and a six-day impounding period, 8-13% TN were recovered in the percolate exhibiting the following composition: 70-80% NH4-N, 25-30% org-N and <1% NOx-N. A large fraction of the influent organic N (55%) was filtered in the bed and 24-29% of initial NH4-N were lost due to nitrification and volatilisation. In permanent impounding systems, 8-11% TN were recovered in the percolate versus 13% in batch-operated beds. N loss was increased with sand layer depth (20-40 cm) under permanent impounding regimes.

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.