Showing papers on "Turbidity published in 2002"

Microbial Load of Drinking Water Reservoir Tributaries during Extreme Rainfall and Runoff

Abstract: Hygienic and microbiological examinations of watercourses are usually not carried out during heavy rainfall and runoff events. After rainfall or snowmelt, there are often massive increases in turbidity in flooding creeks in mountain ranges, which are frequently interpreted as an indication of microbial contamination. The aim of this study was to quantify the microbial loads of watercourses during such runoff events and to compare these loads with loads occurring during regular conditions. In a 14-month monitoring period we investigated the microbial loads of three tributaries of different drinking water reservoirs. A total of 99 water samples were taken under different runoff conditions and analyzed to determine physical, chemical, bacterial, and parasitic parameters. Thirty-two water samples were considered event samples during nine measuring series. The criteria for events, based on duration and intensity of precipitation, water depth gauge measurements, and dynamics, had been fixed before the investigation for each creek individually. Of the physical and chemical parameters examined, only the turbidity, pH, and nitrate values differed clearly from the values obtained for regular samples. Most of the bacteriological parameters investigated (colony, Escherichia coli, coliform, fecal streptococcal, and Clostridium perfringens counts) increased considerably during extreme runoff events. If relevant sources of parasitic contamination occurred in catchment areas, the concentrations of Giardia and Cryptosporidium rose significantly during events. The results show that substantial shares of the total microbial loads in watercourses and in drinking water reservoirs result from rainfall and extreme runoff events. Consequently, regular samples are considered inadequate for representing the microbial contamination of watercourse systems. The procedures for raw water surveillance in the context of multiple-barrier protection and risk assessment ought to include sampling during extreme runoff situations.

Phytoplankton, light, and nutrients in a gradient of mixing depths: field experiments

Abstract: We studied the effects of water column mixing depth and background turbidity on phytoplankton biomass, light climate, and nutrients in two field enclosure experiments designed to test predictions of a dynamical model. In 1997 and 1998, we created gradients of mixing depth by enclosing the 100-μm-filtered phytoplankton community of a phosphorus-deficient lake in cylindrical plastic bags of varying depth (1.5–15 m) which were continuously mixed. To mimic different levels of background turbidity, we surrounded the transparent enclosure walls with a layer of opaque white (1997) or black (1998) plastic. The experiments were run for 4 wk (1997) and 6 wk (1998). The results supported two key assumptions of the model: specific production and specific sedimentation losses both decreased with increasing mixing depth. At all mixing depths, fast-sinking diatoms dominated the communities. In accordance with model predictions, algal biomass concentration and standing stock (summed over the mixed layer) showed a unimodal relationship to mixing depth when background turbidity was high (1998). When background turbidity was lower (1997), only the ascending limbs of the corresponding relationships were found, which supports the prediction that the mixing depth at which biomass peaks (i.e., becomes predominantly limited by light) increases with decreasing background turbidity. Also in accordance with predictions, light intensity at the bottom of the mixed layer decreased with increasing mixing depth and with increasing background turbidity. Finally, the data supported only the ascending limbs of the predicted inverse unimodal relationships among mixing depth and dissolved inorganic and total water column phosphorus. The absence of descending limbs in these relationships at low mixing depths was probably due to deviations of the experimental systems from two model assumptions. First, the remineralization rate of sedimented phosphorus may have been too slow to equilibrate with sedimentation losses over the experimental periods. Second, biomass yield per unit nutrient (the ratio of seston carbon to phosphorus) was not constant, but decreased with increasing mixing depth. To our knowledge, these are the first field experiments in which the effects of mixing depth on phytoplankton and its resources have been investigated systematically along a large gradient.

Impact of an unsealed forest road stream crossing: water quality and sediment sources

Abstract: Turbidity monitoring and rainfall and runoff simulation experiments were conducted at a newly constructed unsealed road stream crossing to determine the quantity and sources of sediment entering the stream. Continuous measurements of turbidity and estimation of total suspended solids (TSS) concentration upstream and downstream of the stream culvert were taken over a 5 month period. There was a statistically significant difference in turbidity and TSS downstream of the crossing during baseflow conditions, but the quality of the water column remained good during non-rain periods. Rainfall events comprised around 20% of the observation period and led to decreases in water quality downstream of the crossing. Water quality could be considered as degraded for 10% of the observations. This was during a period when the rainfall was 65% of the long-term average. Calculated suspended sediment loads were 0·78 t upstream and 2·77 t downstream, an increase of 3·5. It was estimated that at least 2–3 t of bedload material was also added to the stream during the crossing construction and from subsequent erosion. This material is a deposit on the cobble stream bed, and is most likely to degrade aquatic ecosystem values. Rainfall and runoff simulation revealed the principal sediment sources to be a fillslope that contributed coarse bedload material through rill erosion and unprotected toe scour, and the unmetalled road verge that provided fines. Although the quality of water column was good for the majority of the observations, the new Australian and New Zealand Water Quality Guidelines for Fresh and Marine Waters suggest this site exceeded ‘trigger levels’ that would warrant further investigation for both the water column and the bed deposits. Copyright © 2002 John Wiley & Sons, Ltd.

Monitoring dissolved organic carbon in surface and drinking waters

Abstract: The presence of natural organic matter (NOM) strongly impacts drinking water treatment, water quality, and water behavior during distribution. Dissolved organic carbon (DOC) concentrations were determined daily over a 22 month period in river water before and after conventional drinking water treatment using an on-line total organic carbon (TOC) analyzer. Quantitative and qualitative variations in organic matter were related to precipitation and runoff, seasons and operating conditions. Following a rainfall event, DOC levels could increase by 3.5 fold over baseflow concentrations, while color, UV absorbance values and turbidity increased by a factor of 8, 12 and 300, respectively. Treated water DOC levels were closely related to the source water quality, with an average organic matter removal of 42% after treatment.

Phytoplankton, nutrients, and transparency in Danish coastal waters

Abstract: We present a comparative analysis of 1400 data series of water chemistry (particularly nitrogen and phosphorus concentrations), phytoplankton biomass as chlorophylla (chla) concentrations, concentrations of suspended matter and Secchi depth transparency collected from the mid-1980s to the mid-1990s from 162 stations in 27 Danish fjords and coastal waters. The results demonstrate that Danish coastal waters were heavily eutrophied and had high particle concentrations and turbid waters. Median values were 5.1 μg chla 1−1, 10.0 mg DW 1−1 of suspended particles, and Secchi depth of 3.6 m. Chlorophyll concentration was strongly linked to the total-nitrogen concentration. The strength of this relationship increased from spring to summer as the concentration of total nitrogen declined. During summer, total nitrogen concentrations accounted for about 60% of the variability in chlorophyll concentrations among the different coastal systems. The relationship between chlorophyll and total phosphorus was more consistant over the year and correlations were much weaker than encountered for total nitrogen. Secchi depth could be predicted with good precision from measurements of chlorophyll and suspended matter. In a multiple stepwise regression model with In-transformed values the two variables accounted for most of the variability in water transparency for the different seasons and the period March–October as a whole (c. 80%). We were able to demonstrate a significant relationship between total nitrogen and Secchi depth, with important implications for management purposes.

Maximal sustainable sinking velocity of phytoplankton

Abstract: Most phytoplankton species have a tendency to sink. Phytoplankton require light for photosynthesis, however. Therefore, phytoplankton species that sink too fast will not be able to sus- tain a viable population in the euphotic zone. This points to the existence of a maximal sustainable phytoplankton sinking velocity. Using a reaction-advection-diffusion model of phytoplankton growth in a stratified water column, we derive that this maximal sinking velocity is inversely proportional to the turbidity of the water column. In other words, clear waters can sustain species with high sinking rates, whereas turbid waters can sustain species with low sinking rates only. We show that this prediction is both qualitatively and quantitatively supported by empirical data. An intriguing impli- cation is that export production of sinking phytoplankton might be sensitive to the turbidity of the water column.

Effects of Oil Extraction from Moringa Oleifera Seeds On Coagulation Of Turbid Water

Abstract: In this study the results of laboratory based investigation into the effects of extracting oil from Moringa oleifera on its coagulation effectiveness using turbid water samples from two rivers are presented. Samples of raw water were taken from Sungai Selangor Water Treatment Plant at Batang Berjuntai and Sungai Semenyih Water Treatment Plant in Kuala Lumpur, Malaysia. The turbidities of the water samples from the two sources varied from 56 to 451 NTU. For water sample with initial turbidity of 451 NTU, shelled oil extracted Moringa oleifera was able to achieve 98% turbidity removal at an optimum dosage of 200 mg/l compared to 96.9% obtained at optimum dosage of 300 mg/l using the shelled blended. For the low turbidity of 56 NTU, shelled oil extracted Moringa oleifera achieved 87% turbidity removal at 250 mg/L optimum dosage whilst shelled blended was able to achieve 81%. The oil extracted from the Moringa kernel was up to 35% per kernel weight.

Characterisation and concentration profile of aluminium during drinking-water treatment

Abstract: An aluminium(Al) characterisation study was conducted at a surface water treatment plant (Buffalo Pound Water Treatment Plant (BPWTP) in Moose Jaw, Saskatchewan, Canada) to understand better the effect of alum coagulant on various Al fractions. The raw water source for BPWTP is Buffalo Pound Lake water. The Al sources at BPWTP are: • present naturally Al in the raw water and • Al derived due to use of alum as a coagulant. Seasonal evaluations of Al at BPWTP showed that raw lake water total concentrations were highly variable. Suspended (filterable ) Al was the predominant species of raw water total Al. Organic-bound or organo-Al complex Al appeared to be the predominant species of dissolved Al in both raw and treated water during the September to November 1997 Al characterisation study. However, during October to December 1998, inorganic Al dominated dissolved Al content. Characterisation of Al at BPWTP showed that the use of (liquid) Al sulphate (alum) did not increase the concentration of total Al levels. This was because: • alum coagulation was practised at pH 7, at which the Al is least soluble • clarifier and filtration units effectively removed particulate Al and • granular activated carbon (GAC) was capable of removing part of the organic dissolved Al. The study showed that BPWTP would be able to comply with the requirement of Health Canada Guideline value (for conventional treatment plants) for Al of less than 100 μg/ l as total Al. Turbidity and dissolved organic carbon of the raw water influenced the applied alum dose at BPWTP.

Assessment of effluent turbidity in mesophilic and thermophilic activated sludge reactors - origin of effluent colloidal material.

Abstract: Two lab-scale plug flow activated sludge reactors were run in parallel for 4 months at 30 and 55°C. Research focussed on: (1) COD (chemical oxygen demand) removal, (2) effluent turbidity at both temperatures, (3) the origin of effluent colloidal material and (4) the possible role of protozoa on turbidity levels. Total COD removal percentages over the whole experimental period were 66±7% at 30°C and 53±11% at 55°C. Differences in total COD removal between both systems were due to less removal of soluble and colloidal COD at 55°C compared to the reference system. Thermophilic effluent turbidity was caused by a combination of influent colloidal particles that were not effectively retained in the sludge flocs, and erosion of the thermophilic activated sludge itself, as shown by denaturing gradient gel electrophoresis (DGGE) profiles. DGGE analysis of PCR-amplified 16S rDNA fragments from mesophilic and thermophilic sludge differed, indicating that different microbial communities were present in the two reactor systems. The effects of protozoal grazing on the effluent turbidity of both reactors was negligible and thus could not account for the large turbidity differences observed.

Production of Penaeus monodon in the tide fed ponds of Sunderbans

Abstract: Penaeus monodon was cultured in two tide-fed ponds (0.162 ha and 0.184 ha) of Sunderbans, at Kakdwip, India, giving special emphasis to water quality management for sustainable production of shrimp. For first 60 days, filtered and treated tidal water and later untreated water was used for exchange. Water temperature, dissolved oxygen and pH were monitored twice daily, turbidity once in a day. TSS, total alkalinity, salinity, COD and BOD were estimated at weekly intervals. Water exchange was done when turbidity and dissolved oxygen were around 20 cm. and 4mg /1 respectively. During culture, liming @ 75 kg / ha and fertilizers, N and P @ 0.2 PPM each were used for correction of D.O and turbidity problems. During 100 days culture, at a stocking density of 6.7 / sq.m and 7.1 /sq.m, 58.26 % and 58.08 % of stocked seed survived and produced 196 kg and 217 kg of biomass with FCR of 1.150 and 1.173 respectively.

The Turbidity Maximum in a Mesotidal Estuary, the Tamar Estuary, UK: II. The Floc Properties

Abstract: Measurements have been carried out in the turbidity maximum of the Tamar Estuary at neap and spring tides of floc size, settling velocity and effective density. These measurements were complemented by suspended sediment concentration and turbulence profiles. The overall dynamics of the turbidity maximum have been presented in the companion paper (Part I), and form a context for the results presented here. The floc size increased from about 50 to about 350 microns across the turbidity maximum, and settling velocity changed from 0.0-6.0mms −1 . The equivalent change in floc effective density was 50-750kgm −3 . Within the turbidity maximum the proportion of macroflocs (>160microns) increased. The changes in floc properties were correlated with changes in concentration and the turbulence parameter G, the root mean square of the gradient in turbulent velocity fluctuations. An empirical equation representing the settling velocity Ws (mms −1 ) in terms of SPM (mgl −1 ) and G (s −1 ) is: W s = − 0.243 + 0.000567 S P M + 0.981 G − 0.0934 G 2

Novel evaluation method for the water-in-oil (W/O) emulsion stability by turbidity ratio measurements

Abstract: The turbidity ratio method of evaluating the stabilities of water-in-oil emulsions has been established with two wavelengths (450 and 850 nm) by taking the intensity ratio of two beams The slopes of turbidity ratio of several water-in-oil emulsions with time were calculated to evaluate the emulsion stabilities at different HLB (Hydrophilie-Lipophile Balance), the amounts of emulsifiers, and water contents The results of the turbidity ratio technique were consistent with the amount of phase separation of emulsions incubated for 30 days at room temperature From the turbidity ratio measurements, we determined that the required HLB of diesel oil was about 60, and that the stability of emulsion increased with the amount of emulsifier The increasing amount of the water showed a negative effect on emulsion stability Finally, this method provides a useful tool for the quick evaluation of the required HLB and the condition of emulsification throughout this study

Coagulation of high turbidity water: the effects of rapid mixing

Abstract: High turbidity water during the rainy season has long been a challenge to the waterworks in Taiwan. Coagulation is the critical process for solving this problem; however, the dispersion of coagulants in the concentrated solid phase is very difficult. In this study, the effects of rapid mixing on the PACl coagulation of high turbidity water were investigated in terms of turbidity and particle count. Operational parameters of coagulant dosage, coagulant concentration and mixing intensity in the rapid-mixing step exhibited great impacts on the residual turbidity and particle count of the simulated system. Aggregation degree, as evaluated by the Photometric Dispersion Analyser (PDA), was influenced by the intensity of rapid mixing. Poor rapid mixing failed to induce aggregation to effectively coagulate the small and hard to settle particles.

Characteristics of sediment discharge in the subarctic Yukon River, Alaska

Abstract: The characteristics of sediment discharge in the Yukon River, Alaska were investigated by monitoring water discharge, water turbidity and water temperature. The river-transported sediment, 90 wt.% or more, consists of silt and clay (grain size≦62.5 μm), which probably originated in the glacier-covered mountains mostly in the Alaska Range. For early June to late August 1999, we continuously measured water turbidity and temperature near the estuary and in the middle of Yukon River by using self-recording turbidimeters and temperature data loggers. The water turbidity (ppm) was converted to suspended sediment concentration (SSC; mg/l) of river water, using a relation between simultaneous turbidity and SSC at each of the two sites, and then, the suspended sediment discharge, approximately equal to water discharge times SSC, was numerically obtained every 1 or 2 h. It should be noted that the sediment discharge in the Yukon River is controlled by SSC rather than water discharge. As a result, a peak sediment discharge occurred in mid or late August by local sediment runoffs due to glacier-melt (or glacier-melt plus rainfall), while a peak water discharge was produced by snowmelt in late June or early July. Application of the “extended Shields diagram” indicates that almost all the river-transported sediments are under complete suspension.

Optimizing ferric sulfate coagulation of algae with streaming current measurements

Abstract: This study sought to determine ferric sulfate coagulation conditions that lead to effective removal of algae by conventional gravity sedimentation Using laboratory-cultured Anabaena flos-aquae spiked into natural water, charge titrations and jar tests were conducted to evaluate the effects of streaming current value, coagulation pH, and initial algae concentration on the removal of algae, turbidity, and natural organic matter At pH 6, ferric sulfate doses corresponding to the point of zero charge (PZC), as determined by streaming current measurements, consistently produced low settled water algae concentrations when an anionic flocculant aid was added In contrast, ferric sulfate coagulation at pH 70 and 75 was not effective for algae removal because the algae's surface charge could not be sufficiently neutralized At pH 6 and the PZC, settled water algae concentrations, turbidity, and ultraviolet absorbance at 254 nm were similar for tests conducted at initial algae concentrations of 10,000 and 50,000 cells/mL, but a larger coagulant dose was required to reach the PZC at the higher initial algae concentration Thus, adjusting coagulant doses based on streaming current value should be effective for maintaining settled water quality in plants that treat waters with rapidly varying influent algae concentrations and/or background water quality Experiments conducted with a natural algae bloom sample confirmed that ferric sulfate coagulation at pH 6 and the PZC was effective for algae removal