Assessment of E. coli and Salmonella spp. infection risks associated with different fecal sludge disposal practices in Thailand.

The proper management of fecal sludge (FS), to block the transmission pathways of pathogens, is rarely enforced in many parts of the world. Health risks associated with different disposal practices of FS in peri-urban settings of a large metropolis in Thailand were assessed; Tha Klong sub-district with indiscriminate FS dumping, and Klong Luang sub-district which has an FS treatment system. The study showed that indiscriminate FS dumping from along the canal banks and discharge of market waste were likely the major sources of E. coli and Salmonella spp. in contamination of the canal water. The increased microbial pathogen concentrations near the FS treatment facility also indicated contamination risks from poorly designed treatment facilities. Quantitative microbial risk assessment (QMRA) indicated very high water-related infection risk levels compared to the actual locally recorded disease occurrences. These results indicated that the QMRA model needs to be modified to take account of immunological differences between populations in developed countries, where the model was developed, and developing countries. In addition, further sensitivity factors are needed to reflect different societal behavior patterns, and therefore contact with potentially contaminated water, in different sub-populations of many less developed communities.

Municipal wastewater characteristics in Thailand and effects of soft intervention measures in households on pollutant discharge reduction.

In developing countries with large Millennium Development Goals (MDGs) sanitation indicator, pollutant discharge reduction function of wastewater treatment systems should be considered. In this paper, pollutant generations per capita (PGCs) and pollutant discharges per capita (PDCs) are estimated as a base dataset for wastewater management in Thailand. PDCs of black water, i.e. toilet wastewater, are found to be much smaller than PGCs of black water. However, PDCs of gray water, i.e. municipal wastewater other than toilet wastewater are large. Gray water is often discharged without treatment and contributes much to ambient water deterioration. Moreover, possible 5-day biological oxygen demand (BOD5) discharge reductions with "soft interventions", i.e. measurements in households to reduce wastewater pollutant discharge such as using a paper filter or a plastic net in kitchen sinks and so on, are estimated as 39, 21 and 34% for BOD5, total Kjeldahl nitrogen (TKN) and phosphate (PO4-P), respectively. For the estimation, environmental accounting housekeeping (EAH) books of domestic wastewater, spreadsheets with pollutant discharges by water usages and possible effects of "soft interventions" are applied. The framework of this study with "soft intervention" effects on pollutant discharge reductions should enhance wastewater management especially in the areas under development of wastewater treatment systems.

Fractional analysis of arsenic in subsurface-flow constructed wetlands with different length to depth ratios.

Arsenic (As) removal in subsurface-flow constructed wetlands (CW) planting with vetiver grasses was experimented by comparing between two different configurations; (i) deep-bed units (dpCW) with length to depth (L:D) ratio=2 and (ii) shallow-bed units (shCW) with L:D ratio=8; operating at hydraulic retention time (HRT) of 6, 9, and 12 days. The tracer study of CW units revealed that no effect of L:D ratio on dispersion number could be determined, but affecting to the effective volume ratio. Based on the data obtained from the pilot-scale experiments of CW units for 117 days, it is apparent that the dpCW could achieve relatively high As removals (52.9%, 59.2%, and 72.1% at HRT of 6, 9, and 12 days, respectively). Analysis of As mass balance showed that only 0.2-0.4% of As input was uptaken by vetiver grasses whereas the major portion was retained in the CW media (38.9-77.6%). Forms of the retained As was determined by sequential fractionation which could indicate As complexation with iron and manganese on the media surface of 31-38% and As trapping into the media of 42-52% of the total. No obvious difference of As fractions in bed of between dpCW and shCW units was observable.

Nitrogen removal in recirculated duckweed ponds system.

Duckweed-based ponds (DWBPs) have the potential for nitrogen (N) removal from wastewater; however, operational problems such as duckweed die-off regularly occur. In this study, effluent recirculation was applied to the DWBPs to solve the above problem as well as to investigate N removal mechanisms. Two pilot scale recirculated DWBPs were employed to treat municipal wastewater. The average removal efficiencies for TN, TKN and NH4-N were 75%, 89% and 92%, respectively at TN loading of 1.3 g/m2.d and were 73%, 74% and 76%, respectively at TN loading of 3.3 g/m2.d. The effluent of the system under both operational conditions had stable quality and met the effluent standard. Duckweed die-off was not observed during the study, which proves the system stability and effluent recirculation which is thought to be a reason. N-mass balance revealed that nitrification-denitrification and duckweed uptake play major roles in these recirculated DWBPs. The rates of nitrification-denitrification were increased as TN loading was higher, which might be an influence from an abundance of N and a suitable condition. The rates of N uptake by duckweed were found similar and did not depend on the higher TN loading applied, as the duckweed has limited capacity to assimilate it.

Wastewater treatment in tsunami affected areas of Thailand by constructed wetlands.

The tsunami of December 2004 destroyed infrastructure in many coastal areas in South-East Asia. In January 2005, the Danish Government gave a tsunami relief grant to Thailand to re-establish the wastewater management services in some of the areas affected by the tsunami. This paper describes the systems which have been built at three locations: (a) Baan Pru Teau: A newly-built township for tsunami victims which was constructed with the contribution of the Thai Red Cross. Conventional septic tanks were installed for the treatment of blackwater from each household and its effluent and grey water (40 m3/day) are collected and treated at a 220 m2 subsurface flow constructed wetland. (b) Koh Phi Phi Don island: A wastewater collection system for the main business and hotel area of the island, a pumping station and a pressure pipe to the treatment facility, a multi-stage constructed wetland system and a system for reuse of treated wastewater. The constructed wetland system (capacity 400 m3/day) consists of vertical flow, horizontal subsurface flow, free water surface flow and pond units. Because the treatment plant is surrounded by resorts, restaurants and shops, the constructed wetland systems are designed with terrains as scenic landscaping. (c) Patong: A 5,000 m2 constructed wetland system has been established to treat polluted water from drainage canals which collect overflow from septic tanks and grey water from residential areas. It is envisaged that these three systems will serve as prototype demonstration systems for appropriate wastewater management in Thailand and other tropical countries.

Integrated faecal sludge treatment and recycling through constructed wetlands and sunflower plant irrigation.

Faecal sludge (FS) from the on-site sanitation systems is a nutrient-rich source but can contain high concentrations of toxic metals and chemicals and infectious micro-organisms. The study employed 3 vertical-flow CW units, each with a dimension of 5 x 5 x 0.65 m (width x length x media depth) and planted with cattails (Typha augustifolia). At the solid loading rate of 250 kg total solids (TS)/m(2).yr and a 6-day percolate impoundment, the CW system could achieve chemical oxygen demand (COD), TS and total Kjeldahl nitrogen (TKN) removal efficiencies in the range of 80-96%. A solid layer of about 80 cm was found accumulated on the CW bed surface after operating the CW units for 7 years, but no clogging problem has been observed. The CW percolate was applied to 16 irrigation sunflower plant (Helianthus annuus) plots, each with a dimension of 4.5 x 4.5 m (width x length). In the study, tap water was mixed with 20%, 80% and 100% of the CW percolate at the application rate of 7.5 mm/day. Based on a 1-year data in which 3 crops of plantation were experimented, the contents of Zn, Mn and Cu in soil of the experimental plots were found to increase with increase in CW percolate ratios. In a plot with 100% of CW percolate irrigation, the maximum Zn, Mn and Cu concentrations of 5.0, 12.3 and 2.5 mg/kg, respectively, were detected in the percolate-fed soil, whereas no accumulation of heavy metals in the plant tissues (i.e. leaves, stems and flowers) of the sunflower were detected. The highest plant biomass yield and oil content of 1000 kg/ha and 35%, respectively, were obtained from the plots fed with 20% or 50% of the CW percolate.

An integrated electro-chemical and natural treatment system for industrial water pollution control.

Experiments were conducted to test the feasibility of applying an integrated electro-chemical (EC) and natural treatment system for treatment of some industrial wastewaters. The EC process was found to be very effective in removing lead, a model heavy metal from some wastewaters. Within 20 minutes of operation time, 5 to 10 A of electric current and specific surface area of electrode of 46.51 m2/m3, the lead concentrations in the wastewaters were reduced from 35-100 mg/l to less than 1 mg/l. Based on a kinetic model developed from the experimental data, the important parameters for the EC process were found to be electric current, specific surface area of electrode, and operation time. From scanning electron microscopic and X-ray diffractometric (XRD) analysis, the EC sludge samples were found to compose mainly of maghemite (Fe2O3), magnetite (Fe3O4), and laurionite (PbClOH), suitable for disposal to secure landfills. Two pilot-scale constructed wetlands (CW) in series, a model natural treatment system, were employed to treat wastewaters of an industrial estate in Thailand. At organic loading rates of 57-140 kg BOD/hectare-year, these constructed wetlands were able to reduce BOD from 90 to 4 mg/l, while suspended solids, total nitrogen and total phosphorus were reduced from 100 to 10 mg/l, 24 to 4.6 mg/l and 7 to 1.5 mg/l, respectively, during the summer season. These results demonstrated technical feasibility of CW in removing organic and other pollutants contained in this industrial wastewater.

Integrated natural treatment systems for developing communities: low-tech N-removal through the fluctuating microbial pathways.

Integration of natural treatment systems (NTS) (WSP, wetlands etc.) with each other as well as with advanced unit processes (biofiltration) offers a second lease of life to NTS. Long-term full and pilot cale experience in South Africa and Thailand have shown that contrary to a common view, a low tech N-removal from municipal and light industrial wastewater is a reality for a developing community The high treatment efficiency is ascribed to interplay of N-related processes complementing each other. The present FISH-based (Fluorescence In Situ Hybridization) approach to microbial community structure is a pioneering effort in the field of NTS. It establishes interrelationships between major N-removing groups (aerobic and anaerobic ammonia oxidizers (ANAMMOX), denitrifiers) within integrated systems and links them to the high treatment performance. Seasonally fluctuating presence of the ANAMMOX bacteria (0-2.5% of total bacterial numbers) in the NTS (free surface flow wetland) is reported for the first time. Their numbers correlate with metabolically dependent ammonia-oxidizers (2.0-3.0%) but not with stable overall Planctomycetes population (4.5-5.1%). As a result of the flexible microbial structure the robust low cost removal down to TN < 10 mg/L is routinely feasible at the loading rates ranging from 0.005 to 0.08 TN kg/m3/day.

Treatment of septage in constructed wetlands in tropical climate: lessons learnt from seven years of operation.

In tropical regions, where most of the developing countries are located, septic tanks and other onsite sanitation systems are the predominant form of storage and pre-treatment of excreta and wastewater, generating septage and other types of sludges. The septage is disposed of untreated, mainly due to lack of affordable treatment options. This study presents lessons that have been learned from the operation of pilotscale constructed wetlands (CWs) for septage treatment since 1997. The experiments have been conducted by using three CW units planted with narrow-leave cattails (Typha augustifolia) and operating in a vertical-flow mode. Based on the experimental results, it can be suggested that the optimum solids loading rate be 250 kg TS/m2 yr and 6-day percolate impoundment. At these operational conditions, the removal efficiencies of CW units treating septage at the range of 80-96% for COD, TS and TKN were achieved. The biosolid accumulated on the CW units to a depth of 80 cm has never been removed during 7 years of operation, but bed permeability remained unimpaired. The biosolid contains viable helminth eggs below critical limit of sludge quality standards for agricultural use. Subject to local conditions, the suggested operational criteria should be reassessed at the full-scale implementation.

Effects of hydrolysis and carbonization reactions on hydrochar production.

Hydrothermal carbonization (HTC) is a thermal conversion process which converts wet biomass into hydrochar. In this study, a low-energy HTC process named "Two-stage HTC" comprising of hydrolysis and carbonization stages using faecal sludge as feedstock was developed and optimized. The experimental results indicated the optimum conditions of the two-stage HTC to be; hydrolysis temperature of 170 °C, hydrolysis reaction time of 155 min, carbonization temperature of 215 °C, and carbonization reaction time of 100 min. The hydrolysis reaction time and carbonization temperature had a statistically significant effect on energy content of the produced hydrochar. Energy input of the two-stage HTC was about 25% less than conventional HTC. Energy efficiency of the two-stage HTC for treating faecal sludge was higher than that of conventional HTC and other thermal conversion processes such as pyrolysis and gasification. The two-stage HTC could be considered as a potential technology for treating FS and producing hydrochar.

The challenge of faecal sludge management in urban areas--strategies, regulations and treatment options.

In urban centres of industrialising countries, the majority of houses are served by on-site sanitation systems such as septic tanks and unsewered toilets. The faecal sludges (FS) collected from these systems are usually discharged untreated into the urban and peri-urban environment, posing great risks to water resources and to public health. Contrary to wastewater management, the development of strategies to cope with faecal sludges, adapted to the conditions prevailing in developing countries, have long been neglected. The authors describe the current situation and discuss selected issues of FS management. A proposal is made for a rational setting of sludge quality or treatment standards in economically emerging countries. The authors stipulate that regulatory setting should take into account local economic, institutional and technical conditions. Defining suitable treatment options as critical control points in securing adequate sludge quality is better than setting and relying on numerical sludge quality standards. A separate section is devoted to the practice and to regulatory aspects of (faecal) sludge use in Argentina. An overview of treatment options, which may prove sustainable in less industrialized countries is provided. Planted sludge drying beds are one of these options. It has been piloted in Thailand for four years and details on its performance and operation are presented along with data on the hygienic quality of treated biosolids.

Septage dewatering in vertical-flow constructed wetlands located in the tropics.

Constructed wetlands (CWs) have been proven to be an effective low-cost treatment system, which utilizes the interactions of emergent plants and microorganisms in the removal of pollutants. CWs for wastewater treatment are ndrmally designed and operated in horizontal-flow patterns, namely, free-water surface or subsurface flow, while a vertical-flow operation is normally used to treat sludge or septage having high solid contents. In this study, three pilot-scale CW beds, each with a surface area of 25 m2, having 65 cm sand-gravel substrata, supported by ventilated-drainage system and planting with narrow-leave cattails (Typha augustifolia), were fed with septage collected from Bangkok city, Thailand. To operate in a vertical-flow mode, the septage was uniformly distributed on the surface of the CW units. During the first year of operation, the CWs were operated at the solid loading rates (SLR) and application frequencies of, respectively, 80-500 kg total solid (TS)/m2 x yr and 1-2 times weekly. It was found that the SLR of 250 kg TS/m2 x yr resulted in the highest TS, total chemical oxygen demand (TCOD) and total Kjeldahl nitrogen (TKN) removal of 80, 96 and 92%, respectively. The TS contents of the dewatered septage on the CW beds were increased from 1-2% to 30-60% within an operation cycle. Because of the vertical-flow mode of operation and with the effectiveness of the ventilation pipes, there were high degrees of nitrification occurring in the CW beds. The nitrate (NO3) contents in the CW percolate were 180-250 mg/L, while the raw septage had NO3 contents less than 10 mg/L. Due to rapid flow-through of the percolates, there was little liquid retained in the CW beds, causing the cattail plants to wilt, especially during the dry season. To reduce the wilting effects, the operating strategies in the second year were modified by ponding the percolate in the CW beds for periods of 2 and 6 days prior to discharge. This operating strategy was found beneficial not only for mitigating plant wilting, but also for increasing N removal through enhanced denitrification activities in the CW beds. During these 2 year operations, the dewatered septage was not removed from the CW beds and no adverse effects on the septage dewatering efficiency were observed.