Relationship between turbidity and total suspended solids concentration within a combined sewer system

This article confirms the existence of a strong linear relationship between turbidity and total suspended solids (TSS) concentration. However, the slope of this relation varies between dry and wet weather conditions, as well as between sites. The effect of this variability on estimating the instantaneous wet weather TSS concentration is assessed on the basis of the size of the calibration dataset used to establish the turbidity - TSS relationship. Results obtained indicate limited variability both between sites and during dry weather, along with a significant inter-event variability. Moreover, turbidity allows an evaluation of TSS concentrations with an acceptable level of accuracy for a reasonable rainfall event sampling campaign effort.     

SPATIAL AND TEMPORAL CHANGES IN TOTAL SUSPENDED SEDIMENT CONCENTRATIONS IN AN OXBOW LAKE AFTER IMPLEMENTING AGRICULTURAL LANDSCAPE MANAGEMENT PRACTICES

The Wolf–Broad oxbow lake (417 ha) was evaluated by the Mississippi Department of Environmental Quality and included on the Mississippi 303(d) list of impaired waterbodies for total suspended solids (TSS). A study was undertaken for 2 years to evaluate and document changes to TSS (mg L^?1) and overall lake turbidity (NTU) through best management practice implementation. These two objectives were analysed with routine monthly surface sampling events of turbidity (Eureka Manta 2, automated data sonde) as well as 20 random samples per sampling trip for TSS from June 2008 to June 2010. Results from a non‐parametric Kruskal–Wallis analysis indicated a significant month‐by‐year effect on turbidity and TSS (chi‐squared = 76.08, p = 0.001), but reach (chi‐squared = 2.45, p = 0.784) and depth by reach (chi‐squared = 2.44, p = 0.784) did not show significant effects on turbidity. There were no significant correlations between TSS concentrations and turbidity and 2 days and 7 days summed or mean rainfall for the duration of the evaluation. Spearman correlation analysis for TSS indicated significant correlations between TSS and mean two‐day (r² = 0.62, p = 0.002) and seven‐day (r² = 0.51, p = 0.014) wind speeds. All other variables used in the analysis did not show significant correlation with TSS ( p > 0.05). This suggests that wind conditions, rather than rainfall, predict the greatest variability in TSS and turbidity in Wolf Lake. These documented correlations between lake water column TSS, turbidity and wind highlight the difficulties of demonstrating success of management practices in the short temporal period between project initiation and completion. Unmanageable environmental conditions (wind speed and direction) and limited temporal monitoring scales (1 1/2 years post‐BMP implementation) limit the possibility of demonstrating successful water‐quality improvement within a 303(d) listed waterbody such as Wolf Lake. Copyright © 2011 John Wiley & Sons, Ltd.     

TSS concentration in sewers estimated from turbidity measurements by means of linear regression accounting for uncertainties in both variables.

In order to replace traditional sampling and analysis techniques, turbidimeters can be used to estimate TSS concentration in sewers, by means of sensor and site specific empirical equations established by linear regression of on-site turbidity Tvalues with TSS concentrations C measured in corresponding samples. As the ordinary least-squares method is not able to account for measurement uncertainties in both T and C variables, an appropriate regression method is used to solve this difficulty and to evaluate correctly the uncertainty in TSS concentrations estimated from measured turbidity. The regression method is described, including detailed calculations of variances and covariance in the regression parameters. An example of application is given for a calibrated turbidimeter used in a combined sewer system, with data collected during three dry weather days. In order to show how the established regression could be used, an independent 24 hours long dry weather turbidity data series recorded at 2 min time interval is used, transformed into estimated TSS concentrations, and compared to TSS concentrations measured in samples. The comparison appears as satisfactory and suggests that turbidity measurements could replace traditional samples. Further developments, including wet weather periods and other types of sensors, are suggested.     

Comparison of satellite reflectance algorithms for estimating turbidity and cyanobacterial concentrations in productive freshwaters using hyperspectral aircraft imagery and dense coincident surface observations

We analyzed 37 satellite reflectance algorithms and 321 variants for five satellites for estimating turbidity in a freshwater inland lake in Ohio using coincident real hyperspectral aircraft imagery converted to relative reflectance and dense coincident surface observations. This study is part of an effort to develop simple proxies for turbidity and algal blooms and to evaluate their performance and portability between satellite imagers for regional operational turbidity and algal bloom monitoring. Turbidity algorithms were then applied to synthetic satellite images and compared to in situ measurements of turbidity, chlorophyll-a (Chl-a), total suspended solids (TSS) and phycocyanin as an indicator of cyanobacterial/blue green algal (BGA) abundance. Several turbidity algorithms worked well with real Compact Airborne Spectrographic Imager (CASI) and synthetic WorldView-2, Sentinel-2 and Sentinel-3/MERIS/OLCI imagery. A simple red band algorithm for MODIS imagery and a new fluorescence line height algorithm for Landsat-8 imagery had limited performance with regard to turbidity estimation. Blue-Green Algae/Phycocyanin (BGA/PC) and Chl-a algorithms were the most widely applicable algorithms for turbidity estimation because strong co-variance of turbidity, TSS, Chl-a, and BGA made them mutual proxies in this experiment.     

Optimizing the coagulation process in a drinking water treatment plant -- comparison between traditional and statistical experimental design jar tests

In this study of coagulation operation, a comparison was made between the optimum jar test values for pH, coagulant and coagulant aid obtained from traditional methods (an adjusted one-factor-at-a-time (OFAT) method) and with central composite design (the standard design of response surface methodology (RSM)). Alum (coagulant) and polymer (coagulant aid) were used to treat a water source with very low pH and high aluminium concentration at Sri-Gading water treatment plant (WTP) Malaysia. The optimum conditions for these factors were chosen when the final turbidity, pH after coagulation and residual aluminium were within 0-5 NTU, 6.5-7.5 and 0-0.20 mg/l respectively. Traditional and RSM jar tests were conducted to find their respective optimum coagulation conditions. It was observed that the optimum dose for alum obtained through the traditional method was 12 mg/l, while the value for polymer was set constant at 0.020 mg/l. Through RSM optimization, the optimum dose for alum was 7 mg/l and for polymer was 0.004 mg/l. Optimum pH for the coagulation operation obtained through traditional methods and RSM was 7.6. The final turbidity, pH after coagulation and residual aluminium recorded were all within acceptable limits. The RSM method was demonstrated to be an appropriate approach for the optimization and was validated by a further test.     

Decreasing trends in total suspended solids and cumulative effects of nonpoint source projects in the Cuyahoga River Watershed,OH

Using the US EPA’s Grants Reporting and Tracking System (GRTS), we test if completion of best management practices (BMPs) through the Clean Water Act Section (4)319 National Nonpoint Source Program was associated with a decreasing trend in total suspended solids (TSS) load (metric tons/year). The study area chosen had 21 completed projects in the Cuyahoga River watershed in northeastern Ohio from 2000 to 2018. The 4319 projects ranged from dam removal, floodplain/wetland restoration to stormwater projects. There was an overall decreasing trend in TSS loads. We identified three phases of project implementation and completion, where phase 1 had ongoing projects, but none completed (2000–2004). The steepest decrease in loads, identified as phase 2 (2005–2011), was associated with completion of low-head dam modification and removal projects on the mainstem of the Cuyahoga River. A likely decreasing trend was associated with projects completed in the tributaries, such as natural channel design restoration and stormwater green infrastructure (phase 3). Pairing sediment reduction estimates from projects with the river’s flow normalized TSS loading trend, we estimated that the 4319 effort may account for a small fraction of the TSS load reduction. Other stream restoration projects (non-4319) have also been done in the Cuyahoga watershed by other organizations. However, trying to compile these other projects is challenging in larger watersheds having multiple municipalities, agencies, and nonprofits doing restoration without better coordinated record keeping and monitoring. While a decreasing trend in a pollutant load is a desirable water quality outcome, determining what contributed to that trend remains difficult.     

Seasonal,Interannual, and Spatial Variability in the Concentrations of Total Suspended Solids in a Degraded Coastal Wetland of Lake Ontario

A 4-year (1993 through 1996) monitoring program examined the distribution of total suspended solids (TSS) in Cootes Paradise Marsh, a shallow (mean depth of 70 cm), degraded, drownedrivermouth marsh of Lake Ontario. Monthly meteorological and hydrographical data from 1986 through 1996 revealed a hydrologically dynamic system that exhibited large seasonal and interannual variation with respect to precipitation amount, discharge volume, and water levels; the prevailing winds were shown to be oriented along the length of the marsh. Interannual variation in TSS concentrations was inversely related to mean seasonal water levels that fluctuated 45 cm over the 11 years. In a stepwise regression analysis, planktonic chlorophyll-a concentration only explained 2% of the variation in TSS, while inorganic and non-algal organic solids explained 70% and 18%, respectively. Mean seasonal water turbidity increased significantly with mean seasonal wind speed at 17 sampling stations during 1993 and 1994. Runoff from a summer rainstorm more than doubled water turbidities at the mouth of all three creeks over the first 36 hours. In enclosure experiments, water turbidity increased proportionately with biomass of benthivorous fish (especially common carp, Cyprinus carpio). When wind and carp disturbance were compared simultaneously in the field, wind speed accounted for 41% of the variation in turbidity while presence of carp explained an additional 21%. The overall temporal and spatial distribution of TSS in the marsh reflected changes in water level, wind activities, onset of rain events, and fish disturbance that acted in concert to keep Cootes Paradise Marsh extremely turbid throughout the summer.     

Hydrodynamics of longitudinally discontinuous,vertically double layered and partially covered rigid vegetation patches in open channel flow

The aim of this paper is to numerically investigate how the flow structures are affected through a longitudinally discontinuous and vertically two‐layered vegetation occupying half width of the channel, with steady flow rate and subcritical conditions. A three‐dimensional (3‐D) Reynolds stress turbulence model (RSM), incorporated by Computational Fluid Dynamics (CFD) code FLUENT, was first validated with the experimental data, and then used for simulation purpose. The results showed that the flow stream‐wise velocities within the gap regions are visibly slower than that in the vegetation patch regions. Along the cross section, the velocity in the vegetation region (VR) reduced significantly due to resistance offered by the vegetation, which affected the channel conveyance; as compared to the free (non‐vegetated) region. The flow instability in the lateral direction was triggered by the flow shear due to the presence of partly distributed vegetation, resulting in the formation of coherent vortices and exchange of momentum at the interface. The discharge percentage passing through the free region (FR) was found to be 144–525% larger than that passing through the VR. The flow resistance increased significantly with higher vegetation density, whereas it decreased when both the vegetation layers were submerged. Moreover, the flow characteristics profiles in large gaps were more stable than in small gaps. The turbulent kinetic energy (TKE) and turbulence intensity also increased significantly through the patch regions compared to that of the gap regions. The results indicated that the flow structures and the flow resistance are strongly influenced by partial and discontinuous vegetation.     

Vegetation community response to hydrologic and geomorphic changes following dam removal

Dam removal can restore fish passage, natural flow regimes, sediment transport in streams, dispersal of organic matter, and drift of aquatic insects. However, dam removal also impacts the riparian vegetation, with both immediate and delayed responses. In this study, we measure vegetation change at the Merrimack Village Dam site on the Souhegan River in Merrimack, NH, USA. The August 2008 removal caused a ~3‐m drop in water level and rapid erosion of impounded sediment, with ~50% removed in the first 3 months. Terrace, floodplain, and wetland communities were surveyed in summer 2007, 2009, 2014, and 2015. Temporal change was quantified using Analysis of Similarity on the Bray–Curtis dissimilarity matrix. Only herbaceous vegetation closest to the river channel and in the off‐channel wetland changed significantly. The herbaceous plots directly adjacent to the impoundment eroded to bare sand in 2009, but by 2014, the original riparian fringe community had re‐established in the newly developed floodplain. Between 2007 and 2014, the off‐channel wetland area changed from aquatic species to a stable terrestrial community that persisted without significant change in 2015. The vegetation response was greatest in areas with the largest geomorphic and hydrologic change. These included the channel margin where erosion and bank slumping created an unstable scarp. The mid‐channel island and off‐channel wetland were strongly affected by the lowered water table. However, large unvegetated areas never persisted nor did the areal coverage of invasive species expand, which are two frequent concerns of dam removal stakeholders.     

Assessing dry weather flow contribution in TSS and COD storm events loads in combined sewer systems

Continuous high resolution long term turbidity measurements along with continuous discharge measurements are now recognised as an appropriate technique for the estimation of in sewer total suspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In the combined system of the Ecully urban catchment (Lyon, France), this technique is implemented since 2003, with more than 200 storm events monitored. This paper presents a method for the estimation of the dry weather (DW) contribution to measured total TSS and COD event loads with special attention devoted to uncertainties assessment. The method accounts for the dynamics of both discharge and turbidity time series at two minutes time step. The study is based on 180 DW days monitored in 2007-2008. Three distinct classes of DW days were evidenced. Variability analysis and quantification showed that no seasonal effect and no trend over the year were detectable. The law of propagation of uncertainties is applicable for uncertainties estimation. The method has then been applied to all measured storm events. This study confirms the interest of long term continuous discharge and turbidity time series in sewer systems, especially in the perspective of wet weather quality modelling.     

On-site greywater treatment and reuse in multi-storey buildings.

The paper presents a study of a pilot plant treating light greywater for seven flats. The pilot plant combines biological treatment (RBC) with physicochemical treatment (sand filtration and disinfection). The pilot plant produced effluent of excellent quality, meeting the urban reuse quality regulations, and was very efficient in TSS turbidity and BOD removal: 82%, 98% and 96%, respectively. COD removal was somewhat lower (70-75%) indicating that the greywater may contain slowly-biodegradable organics. The RBC (attached growth biological system) was able to retain most of the solids as a result of bioflocculation; further it was proven to have very stable and reliable performance. Faecal coliforms and heterotrophic reductions were very high (100% and 99.99%, respectively) producing effluent that also met drinking water standards. The combination of low organic matter, nutrients and microbial indicators reduces the regrowth and fouling potentials in the reuse system, thus ensuring safe reuse of the treated greywater for toilet flushing.     

Column studies to determine mercury settling in road runoff

A study was performed using a settling column to remove mercury (Hg) from road runoff. The emphasis was placed on the relationship between Hg removal and critical settling velocities, as well as the distribution of total suspended solids (TSS). The impact of rainfall characteristics and temperature on Hg removal was also discussed. Results indicated that Hg removal was significant within the initial 30 min of the settling process. The Hg removal rate increased with the decrease of critical settling velocity, and this trend became gradually significant, which could be used as an important reference for the optimization of sedimentation basin design. Hg removal at different settling times was significantly related to initial distribution of TSS. The impact of rainfall intensity on Hg removal was greater than other parameters of precipitation features, followed by rainfall. In addition, Hg removal was moderately related to temperature. The effect of antecedent dry periods on Hg removal was restricted by rainfall and rainfall intensity.     

Kinetic study of slaughterhouse wastewater treatment by electrocoagulation using Fe electrodes

In this study, treatment of slaughterhouse wastewater by electrocoagulation was investigated in batch system using Fe electrodes. The effect of various variables such as electrode number, current density and operating time was tested. Pollutant removal efficiency increased with increasing electrode number and operating time. The biochemical oxygen demand (BOD(5))(,) chemical oxygen demand (COD), total suspended solid (TSS), and total nitrogen (TN) removal efficiencies using eight electrodes at a contact time of 50 min and a current density of 10 A/m(2) were 66, 62, 60, and 56%, respectively. Higher electrode numbers will allow shorter operating times to achieve certain removal efficiencies. Also, removal efficiencies increased by increasing the current density; the highest removal efficiencies of BOD(5,) COD, TSS, and TN at a contact time of 50 min and a current density of 25 A/m(2) were 97, 93, 81, and 84%, respectively. The results also show that the reactor pH varies directly with the current density; at 25 A/m(2), the reactor pH increased from an initial value of 7.1 to 7.7 after 50 min. The experimental results showed that the kinetics of BOD(5), COD, TSS and TN removal could be fitted adequately using a first order kinetic model (higher R(2)).     

Grey water characterization and treatment for reuse in an arid environment

Grey water from a university facilities building in Cairo, Egypt was analysed for basic wastewater parameters. Mean concentrations were calculated based on grab samples over a 16-month period. Values for chemical oxygen demand (COD) and nutrients exceeded values reported in a number of other studies of grey water, while coliform counts were also high. A submerged membrane bioreactor (SMBR) system using a hollow fibre ultrafiltration membrane was used to treat the grey water with the aim of producing effluent that meets reuse guidelines for agriculture. A test run for 50 days at constant transmembrane pressure resulted in very good removal for key parameters including COD, total suspended solids (TSS), colour, turbidity, ammonia nitrogen, anionic surfactants, and coliform bacteria. High standard deviations were observed for COD and coliform concentrations for both monthly grab samples and influent values from the 50-day SMBR experiment. SMBR effluent meets international and local guidelines for at least restricted irrigation, particularly as pertains to COD, TSS, and faecal coliforms which were reduced to mean treated values of 50 mg/L, 0 mg/L (i.e., not detected), and <50 cfu/100 mL, respectively.     

广州城市河流形态对河流自净能力的影响

构建了包括河道分维数、河道断面形态、河岸基质、河岸带宽度、河岸带植被盖度、河床底质状况、河床栖境复杂性共7项指标的城市河流形态评价体系,并以乌涌广州市开发区段为研究对象,通过定期水质监测研究河流形态对河流自净能力的影响。结果表明,该评价体系能够反映研究河段的形态差异;不同形态河段水体BOD5降解系数及多项水质指标沿程降解率均有显著性差异;河流形态评价得分较高的河段水体自净能力也较强;河流形态与NH3-N、SS、DO和浊度的降解存在相关性,是影响河流自净能力的重要因素。     

Performance of a combined eco-system of ponds and constructed wetlands for wastewater reclamation and reuse.

An on-site study on the operational performance of a combined eco-system of ponds and SF constructed wetland for municipal wastewater treatment and reclamation/reuse in Donging City, Shandong, China was carried out from January 2001 through October 2003. The removal efficiencies for various main parameters were: TSS 84.8 +/- 7.3%, BOD5 87.2 +/- 5.3%, CODCr 70.2 +/- 18.6%, TP 52.3 +/- 23.1%, and NH(3)-N 54.8 +/- 23.9% with effluent concentration of TSS 9.12 +/- 5.12 mg/l, BOD5 6.44 +/- 4.58 mg/l, CODCr, 42.8 +/- 6.7 mg/l, TP 0.94 +/- 0.27 mg/l and NH(3)-N 7.95 +/- 2.36 mg/l. In addition, the removal efficiencies for faecal coliforms and total bacteria were > 99.97% and > 99.998% respectively, which well meet Chinese National standards for effluent quality of municipal wastewater treatment plants. The composition of TSS was closely related to CODCr and BOD5 variations, and nitrification-denitrification is the major mechanism of nitrogen removal both in ponds and in wetlands. In addition, sedimentation also played an important role in the removal of TSS, nitrogen, phosphorus and BOD5. The removal efficiencies of various parameters, the number of species and biomass of biological community in the system increased gradually with the ecological maturation.     

Physical and Biological Responses to an Alternative Removal Strategy of a Moderate‐sized Dam in Washington,USA

Dam removal is an increasingly practised river restoration technique, and ecological responses vary with watershed, dam and reservoir properties, and removal strategies. Moderate‐sized dams, like Hemlock Dam (7.9 m tall and 56 m wide), are large enough that removal effects could be significant, but small enough that mitigation may be possible through a modified dam removal strategy. The removal of Hemlock Dam in Washington State, USA, was designed to limit channel erosion and improve fish passage and habitat by excavating stored fine sediment and reconstructing a channel in the former 6‐ha reservoir. Prior to dam removal, summer daily water temperatures downstream from the dam increased and remained warm long into the night. Afterwards, a more natural diel temperature regime was restored, although daily maximum temperatures remained high. A short‐lived turbidity pulse occurred soon after re‐watering of the channel, but was otherwise similar to background levels. Substrate shifted from sand to gravel–cobble in the former reservoir and from boulder to gravel–cobble downstream of the dam. Initially, macroinvertebrate assemblage richness and abundance was low in the project area, but within 2 years, post‐removal reaches upstream and downstream of the dam had diverse and abundant communities. The excavation of stored sediment and channel restoration as part of the dam removal strategy restored river continuity and improved benthic habitat while minimizing downstream sedimentation. This study provides a comparison of ecological effects with other dam removal strategies and can inform expectations of response time and magnitude. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

强化混凝技术处理南淝河污染水的效果

选用聚合氯化铁(PFC)、聚合硫酸铁(PFS)、聚合氯化铝(PAC)和聚合氯化铝铁(PAFC)作为混凝剂;选用阳离子型聚丙烯酰胺(CPAM)、阴离子型聚丙烯酰胺(APAM)和非离子型聚丙烯酰胺(NPAM)作为助凝剂,通过室内试验对比研究强化混凝技术中多种混凝剂单用及其和助凝剂联用对南淝河污染水的除浊和去污效果,并用于南淝河现场构建的混凝沉淀系统。结果表明,4种混凝剂单用时,PAFC对浊度、TP去除效果最优,对CODMn有良好的去除效果,且不影响原水的p H值,而PFC和PFS单用时可明显降低原水p H值,4种混凝剂单用时对TN均没有明显去除效果;PAFC与CPAM联用时对浊度的去除效果最佳,明显优于PAFC与APAM和NPAM联用和PAFC单用的效果;混凝剂与CPAM联用提高了其除浊和去除TP的能力,但不能明显改善其去除CODMn的效果,对原水p H和TN的影响与单用时相同。选取"PAFC+CPAM"作为南淝河示范工程的混凝剂和助凝剂,现场混凝沉淀出水水质稳定,浊度和TP的去除效果较好,去除率分别达到90%和80%,对CODMn的去除率约为52%,而对TN的去除效果有限,去除率约为22.4%。     

复式河槽漫滩水流的三维数值计算

采用紊流模型中的雷诺应力模型(RSM)对非对称复式河槽水流的三维紊流进行了数值模拟。数值模拟计算结果与试验结果的比较表明RSM能够很好地模拟滩槽交互区内的二次流、主流速分布和床面剪切力,此模型模拟复式河槽是可靠的。最后用RSM模拟了对称复式河槽在不同水深下的流速场及床面剪切力分布,得出当水深增加时,滩槽交互区二次流动纵向涡增强,而浅滩主流速及床面剪切力迅速增大的结论。     

PHYSICAL AND PLANT COMMUNITY CONTROLS ON NITROGEN AND PHOSPHORUS LEACHING FROM IMPOUNDED RIVERINE WETLANDS FOLLOWING DAM REMOVAL

Dam removal has emerged as a critical issue in water resources engineering and management. Of particular concern in many regions of the USA is the effect of dam removal on downstream water quality and potential methods of decreasing sediment and nutrient loading to downstream reaches. Rapid revegetation of reservoir sediments has been suggested as a means of reducing the impact of dam removal, although little data exist about the role of vegetation in controlling the downstream release of sediment or nutrients. This study investigated an impounded riverine wetland complex on the Little River, North Carolina, before and after the removal of a low‐head dam. We quantified the leaching of interstitial nitrogen (N) and phosphorus (P) to the adjacent river channel during reservoir dewatering and, through experimental manipulations, isolated the difference between physical (soil) and biological (plant) controls on N and P leaching from dewatering impoundment sediments. We found that the rate and the quantity of N and P leaching from impounded dewatering sediment are predominately controlled by sediment porosity and specific yield. Although vegetation controls on N and P leaching were statistically significant during the first growing season following dam removal, vegetation is likely to be more important as a long‐term control on sediment and nutrient loads. Our results suggest that the initial release of N and P from a dewatered reservoir will be difficult to control but that vegetation may play an important long‐term role. Copyright © 2011 John Wiley & Sons, Ltd.