Tropical Urban Catchment Research Articles

Temporal variation of faecal indicator bacteria in tropical urban storm drains

Human faecal contamination poses a widespread hazard for human health. In urban areas, sewer leakage may be an important cause of faecal pollution to surface water. Faecal indicator bacteria (FIB) are the most widely used indicators to monitor surface water quality. However, assessing whether a water body is meeting water quality criteria is made difficult by the high variability of FIB concentrations over time. In this study, the variation of FIB concentration in surface water from tropical urban catchments is investigated. Eleven urban sub-catchments were sampled hourly over 24-hr and samples analysed for FIB. It was found that FIB show a diurnal pattern that is characterised by daytime FIB concentrations that are significantly higher than nighttime FIB concentrations. This observed diurnal variation of FIB closely follows that of sewer flows and contrasts with observations in rural streams where FIB concentrations are known to be low in the daytime and high during the night. Field tracer tests provide qualitative evidence of sewage exfiltration and transport to drains via preferential flow paths. The diurnal FIB variation and field tracer tests indicate the likelihood of surface water contamination due to leaking sewers. The results further suggest that contamination of surface-water drains is likely a widespread problem in tropical urban areas due to extensive drainage networks and the persistence of FIB under tropical conditions. Because of FIB variation over time, the time at which samples are collected is important in being able to capture the daily maximum and minimum FIB concentrations. The Kruskal–Wallis test shows that hourly sampling from 04:00 to 07:00 and from 12:00 to 15:00 results in significantly different FIB concentration (minimum and maximum, respectively). Furthermore, the Wilcoxon-Mann-Whitney test shows that sampling at 12:00 and 14:00 results in significantly higher FIB concentrations, while sampling at 05:00 and 04:00 or 05:00 and 06:00 results in significantly lower FIB concentrations, than sampling at other hours of the day.

Sizing first flush pollutant loading of stormwater runoff in tropical urban catchments

This study aimed at investigating the first flush phenomenon from residential, commercial and industrial catchments. Stormwater was grab sampled and the flow rate was measured during 52 storm events. The dimensionless cumulative pollutant mass and runoff volume were used to determine the runoff volume needed to transport 50 and 80 % of total pollutant mass. Almost all the constituents did not satisfy this first flush definition except for total suspended solids (TSS) in the commercial catchment. The averages first runoff volume required to remove 50 and 80 % of the total pollutant mass were 37 and 67, 35 and 65, and 36 and 64 % for the residential, commercial and industrial catchments, respectively. It seemed that less runoff is required to transport the same amount of pollutant loadings in tropical urban catchments than in temperate regions. BOD, COD, NH3-N, SRP and TP consistently showed strong first flush effects in all catchments. The first flush strengths of TSS, BOD, COD, NH3-N and TP in the commercial catchment were strongly correlated with total rainfall, rainfall duration, max 5 min intensity, runoff volume and peak flow, but not with antecedent dry days. Management of the first 10 mm runoff depth would be able to capture about half of the total pollutant mass in stormwater runoff that would otherwise goes to drains.

Surveillance of enteric viruses and coliphages in a tropical urban catchment

An assessment of the occurrence and concentration of enteric viruses and coliphages was carried out in highly urbanized catchment waters in the tropical city-state of Singapore. Target enteric viruses in this study were noroviruses, adenoviruses, astroviruses and rotaviruses. In total, 65 water samples were collected from canals and the reservoir of the Marina catchment on a monthly basis over a period of a year. Quantitative PCR (qPCR) and single agar layer plaque assay (SAL) were used to enumerate target enteric viruses and coliphages in water samples, respectively. The most prevalent pathogen were noroviruses, detected in 37 samples (57%), particularly norovirus genogroup II (48%), with a mean concentration of 3.7 × 102 gene copies per liter. Rotavirus was the second most prevalent virus (40%) with a mean concentration of 2.5 × 102 GC/L. The mean concentrations of somatic and male-specific coliphages were 2.2 × 102 and 1.1 × 102 PFU/100 ml, respectively. The occurrence and concentration of each target virus and the ratio of somatic to male-specific coliphages varied at different sampling sites in the catchment. For sampling sites with higher frequency of occurrence and concentration of viruses, the ratio of somatic to male-specific coliphages was generally much lower than other sampling sites with lower incidences of enteric viruses. Overall, higher statistical correlation was observed between target enteric viruses than between enteric viruses and coliphages. However, male-specific coliphages were positively correlated with norovirus concentrations. A multi-level integrated surveillance system, which comprises the monitoring of bacterial indicators, coliphages and selected enteric viruses, could help to meet recreational and surface water quality criteria in a complex urbanized catchment.

Characterization and source identification of stormwater runoff in tropical urban catchments

The characteristics of urban stormwater pollution in the tropics are still poorly understood. This issue is crucial to the tropical environment because its rainfall and runoff generation processes are so different from temperate regions. In this regard, a stormwater monitoring program was carried out at three urban catchments (e.g. residential, commercial and industrial) in the southern part of Peninsular Malaysia. A total of 51 storm events were collected at these three catchments. Samples were analyzed for total suspended solids, 5-day biochemical oxygen demand, chemical oxygen demand (COD), oil and grease, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen (NH3-N), soluble reactive phosphorus and total phosphorus. Principal component analysis (PCA) and hierarchical cluster analysis were used to interpret the stormwater quality data for pattern recognition and identification of possible sources. The most likely sources of stormwater pollutants at the residential catchment were from surface soil and leachate of fertilizer from domestic lawns and gardens, whereas the most likely sources for the commercial catchment were from discharges of food waste and washing detergent. In the industrial catchment, the major sources of pollutants were discharges from workshops and factories. The PCA factors further revealed that COD and NH3-N were the major pollutants influencing the runoff quality in all three catchments.

Storm runoff quality and pollutant loading from commercial, residential, and industrial catchments in the tropic

Information on the pollution level and the influence of hydrologic regime on the stormwater pollutant loading in tropical urban areas are still scarce. More local data are still required because rainfall and runoff generation processes in tropical environment are very different from the temperate regions. This study investigated the extent of urban runoff pollution in residential, commercial, and industrial catchments in the south of Peninsular Malaysia. Stormwater samples and flow rate data were collected from 51 storm events. Samples were analyzed for total suspended solids, 5-day biochemical oxygen demand, chemical oxygen demand, oil and grease (O&G), nitrate nitrogen (NO3-N), nitrite nitrogen, ammonia nitrogen, soluble reactive phosphorus, total phosphorus (TP), and zinc (Zn). It was found that the event mean concentrations (EMCs) of pollutants varied greatly between storm characteristics and land uses. The results revealed that site EMCs for residential catchment were lower than the published data but higher for the commercial and industrial catchments. All rainfall variables were negatively correlated with EMCs of most pollutants except for antecedent dry days (ADD). This study reinforced the earlier findings on the importance of ADD for causing greater EMC values with exceptions for O&G, NO3-N, TP, and Zn. In contrast, the pollutant loadings are influenced primarily by rainfall depth, mean intensity, and max 5-min intensity in all the three catchments. Overall, ADD is an important variable in multiple linear regression models for predicting the EMC values in the tropical urban catchments.

Level and transport pattern of faecal coliform bacteria from tropical urban catchments

Urbanization and frequent storms play important roles in increasing faecal bacteria pollution, especially for tropical urban catchments. However, only little information on the faecal bacteria levels from different land use types and the factors that influence bacteria concentrations is available. Thus, the objectives of this study were to quantify the levels and transport mechanism of faecal coliforms (FCs) from residential and commercial catchments. Stormwaters were sampled and the runoff flow rates were measured from both catchments during four storm events in Skudai, Malaysia. The samples were then analysed for FC, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS) and ammoniacal-nitrogen (NH3-N) concentrations. Intra-storm and inter-storm characteristics of FC bacteria were investigated in order to identify the level and transport pattern of FC. The commercial catchment showed significantly higher event mean concentration (EMC) of FC than the residential catchment. For the residential catchment, the highest bacterial concentrations occurred during the early part of stormwater runoff with peak concentrations usually preceding the peak flow. First flush effect was more prevalent at the residential catchment.

Optimization of pollution control performance of wet detention ponds in tropical urban catchments using particle swarm optimization

Wet detention ponds are the best management systems for the control of urban stormwater. The objective of this study is to develop optimum pollution control performance of wet detention ponds using an analytical probabilistic model (APM) and particle swarm optimization (PSO). An urban catchment, in a tropical region, was selected as a case study and APM parameters were developed using long-term rainfall data. Firstly, the active storage was kept constant while the permanent pool was varied and PSO simulations conducted. Secondly, PSO simulations were conducted, keeping the permanent pool constant and varying the active storage. The pollution control increased with increasing detention time, reached a peak value and thereafter declined. However, the pollution control was more sensitive to permanent pool than active storage as higher pollution control is attained at a shorter time using the former. The PSO captures the optimum detention time and the corresponding peak pollution control performance by five iterations and the computational time required for the PSO is much shorter than the APM which has to be exhaustively enumerated. The optimum detention time in tropical climates is found to be shorter than temperate regions and recommendations given in existing literature cannot be applied to tropical regions.

Modelling runoff quantity and quality in tropical urban catchments using Storm Water Management Model

Due to differences in rainfall regimes and management practices, tropical urban catchments are expected to behave differently from temperate catchments in terms of pollutant sources and their transport mechanism. Storm Water Management Model (SWMM) was applied to simulate runoff quantity (peakflow and runoff depth) and quality (total suspended solids and total phosphorous) in residential, commercial and industrial catchments. For each catchment, the model was calibrated using 8–10 storm events and validated using seven new events. The model performance was evaluated based on the relative error, normalized objective function, Nash–Sutcliffe coefficient and 1:1 plots between the simulated and observed values. The calibration and validation results showed good agreement between simulated and measured data. Application of Storm Water Management Model for predicting runoff quantity has been improved by taking into account catchment’s antecedent moisture condition. The impervious depression storages obtained for dry and wet conditions were 0.8 and 0.2 mm, respectively. The locally derived build-up and wash-off parameters were used for modelling runoff quality.

HYDROLOGICAL CHARACTERISTICS THAT DETERMINE SUSPENDED SEDIMENT LOAD OF TROPICAL URBAN STORM EVENTS

Dwelling on the less investigated tropical urban river channels, this paper attempts to understand the hydrological characteristics that dominate and account for most of the suspended loads of individual events through intra-events SS concentrations-Discharge (Q) relationship. Individual storm event has a variable signature due to the differing hydrological characteristics. As such, suspended sediment (SS) loads transported during storm events are never equivalent. A total of 34 storm events were determined from four gauging stations in the Kallang subcatchment, of the Marina Barrage Catchment, Singapore. There is a need for authorities to understand the nature of storm dynamics for optimal management of water resources in the new reservoir’s catchment. Step-wise regression model was used to determine the dominating hydrological characteristics of the total loads during the storm events. Peak SS concentrations and the duration of high rainfall intensity (>60mm/h) are the main determinant of SS loads in the tropical urban waterways. Rapid rising and falling limbs of the storm hydrograph and short, intense storm events, typical of tropical, urban environment are explanations for the outcomes attained from the regression analysis. (Keywords: Tropical urban catchment, Suspended Sediment, Discharge, Regression modeling, Hydrological Characteristics ) INTRO

Occurrence of emerging organic contaminants in a tropical urban catchment in Singapore

Emerging organic contaminants (EOCs) occurring in urban runoff can negatively impact sensitive ecosystems and drinking water resources. The occurrence of 13 EOCs was characterized in the Marina Catchment, a large urban catchment approximately one-sixth the area of Singapore. The 13 EOCs included alkylphenol ethoxylate metabolites (APEMs), hormones, pharmaceuticals, bisphenol A, and a pesticide (fipronil). The APEMs were most prevalent with concentrations of nonylphenol ethoxyacetic acid (NP1EC) and nonlyphenol (NP) ranging from several ng L −1 to 6 μg L −1 and 4 μg L −1, respectively, while concentrations of octylphenol ethoxyacetic acid (OP1EC), dicarboxylated alkylphenol ethoxyacetic acid (CA3P1EC, CA4P1EC) were as high as 0.9 μg L −1. Other EOCs were present in the ng L −1 range: chloramphenicol 1–15 ng L −1, ibuprofen 2–76 ng L −1, naproxen 8–108 ng L −1, bisphenol A 30–625 ng L −1, fipronil 1–72 ng L −1, estrone 1–304 ng L −1, estriol 3–451 ng L −1. The APEMs and EOCs detected appear to enter canals and rivers from non-point sources, possibly from runoff and leaking sewer lines. The closure of Marina Bay with a barrage has resulted in significantly higher levels of APEMS compared to when the bay was open to the sea. Depth profiles show that NP1EC and OP1EC were notably lower in deep waters compared to surface waters. NP, estrone and estriol exceeded literature-based Predicted No Effect Concentration (PNEC) values.

Prevalence and genetic diversity of waterborne pathogenic viruses in surface waters of tropical urban catchments

To study the virological quality of surface water from highly urbanized tropical water catchment areas and to determine predominant enteric viral genotypes in surface water. A wide range of human pathogenic viruses in urban surface waters was screened by nested PCR assays after concentration by ultrafiltration. Among the 84 water samples collected, at least one virus was detected in 70 (83·3%) of these samples. Noroviruses were determined to be the most prevalent enteric viruses detected in urban surface water samples, followed by astroviruses, enteroviruses, adenoviruses and hepatitis A viruses. The molecular characterization of environmental viral isolates suggested co-circulation of multiple genotypes of both noroviruses GI and GII, astroviruses and enteroviruses in urban surface waters. Human enteric viruses with great genetic diversity were detected in surface waters, indicating the presence of human origin of faecal contamination in highly urbanized water catchment areas.

Prevalence and Genotypes of Human Noroviruses in Tropical Urban Surface Waters and Clinical Samples in Singapore

The prevalence and genotypes of norovirus genogroup I (GI) and GII in tropical urban catchment waters and an estuarine bay were studied. A comparative analysis was performed with environmental isolates of noroviruses and concurrently identified clinical isolates in Singapore during gastroenteritis outbreaks between August 2006 to January 2007. Noroviruses in environmental water samples were concentrated by using ultrafiltration techniques and then analyzed by reverse transcription-seminested PCR assay targeting the partial capsid region of noroviruses and DNA sequencing. Among the 60 water samples collected, noroviruses were detected in 43 (71.7%) of these samples. Of these 43 norovirus-positive samples, the coexistence of both GI and GII strains was identified in 23 (53.5%) water samples. The phylogenetic analysis revealed multiple genotypes of noroviruses GI and GII in environmental water samples. GI and GII strains were clustered into seven and nine (including two unclassified) genotypes, respectively. The major norovirus genotypes in environmental water samples were GI/2 and GI/4 and GII/4. Genotyping of the 21 norovirus-positive clinical samples showed that all of the strains belonged to the GII/4 cluster. The environmental and clinical norovirus GII/4 isolates showed high levels of nucleotide sequence identity to each other and to the novel GII/4 variant associated with global epidemics of gastroenteritis during 2006. This study suggests the emergence and circulation of multiple novel norovirus GI and GII genotypes in water environments. Further comprehensive surveillance of water environments for noroviruses and routine clinical reporting is warranted.

“In Line” Combined Storm and Wastewater Treatment System for Tropical Urban Drainage Catchments

This paper presents a conceptualized combined storm and wastewater treatment system for typical low income, high density drainage catchment similar to the case of Manila City. In many developing and tropical port cities in low-lying floodplains, local and regional floods and non sewered communities compound in a problem that manifests in surface water pollution. This results in particularly difficult situation to introduce major sewerage infrastructure and a centralized wastewater treatment system. Thus, to initiate and invite discussions on different and possible solutions is necessary to address the need to provide appropriate treatment systems in rapidly growing cities and urban populations. This paper aims to contribute to such discussions by suggesting possible treatment processes achievable in limited, under exploited spaces in urban drainage networks. Also the paper mentions systematic estimations relevant to assess and theoretically simulate suggested treatment system. Following Hvitved-Jacobsen etal (2002) recognition of the role of sewers as bioreactors, the proposed system takes reviewed physical and biological techniques to be installed parallel to the track of drainage channels that provides neither on-site nor off-site approaches, but “inline” treatment. Essentially, the system integrates sewers or drains in the entire treatment system. The estimated primary and secondary information on both physical and socio-economic parameters in the study site, and the adapted “alternative” principles of decentralized, small scale systems yielded a multiple site designs including the following treatment processes and units: 1) inline fine and micro screening; 2) vegetated submerged beds (VSB); 3) rotating biological contactors (RBC); and 4) “biotowers”. All were designed to capture and reduce typical wastewater constituents (TSS, BOD, TKN and Coliforms) continuously during “dry” and “average wet” conditions until year 2025. The system embodies an effective and alternative wastewater treatment system for Philippine effluent standards, replicable in other tropical urban drainage catchments.

Runoff quality and pollution loadings from a tropical urban catchment

Runoff quality draining from 17.14 km2 urban catchment in Johor Bahru, Malaysia, was analysed. The land-use consists of residential (30.3%), agricultural (27.3%), open space (27.9%), industrial (8.1%) and commercial (6.4%) areas. Three storm events were sampled in detail. These storms produced stormflow between 0.84 mm and 27.82 mm, and peakflow from 2.19 m3/s to 42.36 m3/s. Water quality showed marked variation during storms especially for TSS, BOD and COD with maximum concentrations of 778 mg/l, 135 mg/l and 358 mg/l, respectively. Concentrations of TOC, DOC, NH3-N, Fe and level of colour were also high. In general, the river quality is badly polluted and falls in Class V based on the Malaysian Interim National Water Quality Standards. Event Mean Concentrations (EMC) for various parameters varied considerably between storms. The largest storm produced higher EMC for TSS, NO3-N and SS whereas the smaller storms tend to register higher EMC for BOD, COD, NH3-N, TOC, Ca, K, Mg, Fe and Zn. Such variations could be explained in terms of pollutant availability and the effects of flushing and dilution. Based on a three-month average recurrence interval (ARI) of rainfall, the estimated event loadings (ton/ha) of TSS, BOD, COD, TOC, NH3-N and NO3-N were 0.055, 0.016, 0.012, 0.039, 0.010, 0.0007 and 0.0002, respectively. Heavy metals present in trace quantities. Storms with 3 months ARI could capture about 70% of the total annual loads of major pollutants.