High Concentrations Of Suspended Solids Research Articles

Suspended Solids Removal Efficiencies of a Barrier Board that Pre-Treats High-Turbidity Raw Water

It tends to produce high-turbidity raw water during the initial period of typhoons or storms and affect the operation of the purifying system. In this research, Raw water suspended solids roughly to 5,000-9,000 mg/l, the removal rate can be to about 70%-90 %, and reduced to 800 mg/l or less, 8 ml/s minimum about 100-400 mg/l. Overall, the quality of effluent water with the overflow water height increased removal rate rose gradually reduce the suspended solids concentration, gravity settling and effective appear, especially the section Ⅳ region (40 cm) removal are more than 80 %, flow 100 ml/s to 84 %, compared with I (10 cm) with 100 ml/s for 74 %, with obvious benefits. The overflow height of the flow of 8 ml/s, and suspended solids by the inlet concentration at 7,400 mg/l to 8,700 mg/l, down to the effluent concentrations are below 300 mg/l, which overflow height of 20, 30, and 40 cm can be reduced to below 200 mg/l, showing that gravitational sedimentation can significantly remove the high concentration of suspended solids.

Occurrence, fate, and fluxes of perfluorochemicals (PFCs) in an urban catchment: Marina Reservoir, Singapore

A study was carried out to characterize the occurrence, sources and sinks of perfluorochemicals (PFCs) in the Marina Catchment and Reservoir, Singapore. Salinity depth profiles indicated the reservoir was stratified with lower layers consisting of sea water (salinity ranging from 32 to 35 g L(-1)) and a brackish surface layer containing approximately 14-65% seawater. The PFC mixture detected in catchment waters contained perfluoroalkyl carboxylates (PFCAs), particularly perfluorooctanoate (PFOA), perfluorohexanoate (PFHpA), perfluorooctane sulfonate (PFOS) and PFC transformation products. PFC concentrations in storm runoff were generally higher than those in dry weather flow of canals and rivers. PFC concentration profiles measured during storm events indicated 'first flush' behavior, probably because storm water is leaching PFC compounds from non-point sources present in the catchment area. Storm runoff carries high concentrations of suspended solids (SS), which suggests that PFC transport is via SS. In Marina Bay, PFCs are deposited in the sediments along with the SS. In sediments, the total PFC concentration was 4,700 ng kg(-1), approximately 200 times higher than in the bottom water layers. Total perfluoroalkyl sulfonates (PFSAs), particularly PFOS and 6:2 fluoro telomer sulfonate (6:2 FtS) were dominant PFCs in the sediments. PFC sorption by sediments varied with perfluorocarbon chain length, type of functional group and sediment characteristics. A first approximation analysis based on SS transport suggested that the annual PFC input into the reservoir was approximately 35 ± 12 kg y(-1). Contributions of SS, dry weather flow of river/canals, and rainfall were approximately 70, 25 and 5%, respectively. This information will be useful for improving strategies to protect the reservoir from PFC contamination.

Anaerobic digestion of cheese dairy wastewater following chemical oxidation

As global cheese production has gradually increased there has been a proportional increase in the wastewater produced which poses serious environmental problems. Conventional anaerobic treatment processes are often used for dairy wastewaters. However, lipids inhibition and high suspended solids concentrations are the main operational problems for anaerobic digesters treating dairy wastewater. The performance of a pilot scale cheese production wastewater treatment plant that includes an oxidation pretreatment stage and a UASB (upflow anaerobic sludge blanket) reactor was investigated. Monitoring was performed during the start-up period, the fully operational period and the period following wastewater depletion. The data from this six month period are presented and evaluated. The mean composition of raw wastewater was: chemical oxygen demand (COD) 20,314 mg l −1 , total organic carbon (TOC) 7920 mg l −1 , total Kjeldahl nitrogen (TKN) 285 mg l −1 , total phosphate (TP) 85 mg l −1 , fats 1931 mg l −1 and pH 4. In the oxidation pretreatment stage fats presented a significant reduction that reached 80% and the sharp peaks of the all pollution parameters of the raw wastewater were adequately smoothed. The anaerobic digester performance was considered satisfactory, since the COD reduction >90%. A significant fraction of the input carbon was retained in the sludge bed as “absorbed” carbon and then hydrolysed slowly following first order kinetics with a hydrolysis rate constant of 0.0036 d −1 . The pilot plant operation showed that the proposed technology could be sustainable not only in terms of the treatment of cheese-dairy wastewater but for their energy utilisation as well. ► Fenton oxidation improved the biodegradability of the wastewater. ► Significant fats reduce was reported. ► The pollution parameters fluctuations were smoothed. ► The TOC reduction in the UASB was over 90%. ► The produced biogas had a high methane content.

Impacto de sistemas de produção pecuários/agrícolas na qualidade da água da sub bacia do rio pinhal, santa catarina, brasil

O Brasil é um dos maiores produtores de alimentos do mundo. As produções agrícolas e animais estão concentradas em determinadas regiões do país. A pecuária tem sido percebida como uma ameaça constante para a quantidade e a qualidade dos recursos hídricos. O objetivo deste estudo foi avaliar o impacto de sistemas de produção pecuários/agrícolas na qualidade da água superficial na sub-bacia do Rio Pinhal que está localizado em Concórdia, Santa Catarina. Oito pontos de amostragem, representando diferentes usos da terra (LU1: gado leiteiro; LU2: sem animais; LU3: gado leiteiro + porcos + aves de corte + culturas; LU4: porcos + aves de corte + culturas; LU5: gado leiteiro + porcos + aves de corte + culturas + humanos; LU6: gado leiteiro + porcos + culturas; LU7 e LU8: gado leiteiro + porcos) foram avaliados. As águas foram amostradas durante o verão, outono, primavera e inverno de 2006 a 2009. LU1 apresentou a pior qualidade da água com altas concentrações de sólidos suspensos totais (SST) e demanda química de oxigênio. Neste ponto, os animais tinham acesso ao rio. A maior concentração de nitrato (NO3-N) foi encontrada na foz do rio. Houve maiores concentrações de SST, NO3-N e NO2-N na estação chuvosa. Nesta estação há intensiva aplicação de fertilizantes orgânicos para os campos de milho. Outono e inverno apresen-taram a pior qualidade da água em relação à concentração de nitrogênio. Os resultados mostraram forte relação entre as fontes de poluição e qualidade da água. O gerenciando o uso de fertilizantes orgânicos com o de fertilizantes químicos e a recuperação das áreas ripárias são ações mitigatórias importantes para proteger a qualidade da água do rio Pinhal.

Experimental investigation on water quality standard of Yangtze River water source heat pump

Due to the surface water in the upper reaches of Yangtze River in China containing large amounts of silt and algae, high content of microorganisms and suspended solids, the water in Yangtze River cannot be used for cooling a heat pump directly. In this paper, the possibility of using Yangtze River, which goes through Chongqing, a city in southwest China, as a heat source-sink was investigated. Water temperature and quality of the Yangtze River in the Chongqing area were analyzed and the performance of water source heat pump units in different sediment concentrations, turbidity and algae material conditions were tested experimentally, and the water quality standards, in particular surface water conditions, in the Yangtze River region that adapt to energy-efficient heat pumps were also proposed. The experimental results show that the coefficient of performance heat pump falls by 3.73% to the greatest extent, and the fouling resistance of cooling water in the heat exchanger increases up to 25.6% in different water conditions. When the sediment concentration and the turbidity in the river water are no more than 100 g/m3 and 50 NTU respectively, the performance of the heat pump is better, which can be used as a suitable river water quality standard for river water source heat pumps.

강수조건에 따른 도암호 부유물질 거동 평가

BACKGROUND: The Doam watershed in Korea has been managed for the reduction and the prevention of non-point source pollution since 2007. Especially, the water quality of the Doam reservoir is a primary issue related to the Doam dam reoperation. We have carried out the modeling to evaluate the water quality based on suspended solids (SS) of the Doam watershed and the Doam reservoir. Two powerful hydrological and water quality models (HSPF and CE-QUAL-W2) were employed to simulate the combined processes of water quantity and quality both in the upland watershed of the Doam reservoir and the downstream waterbody. METHODS AND RESULTS: The HSPF model was calibrated and validated for streamflow and SS. The CE-QUAL-W2 was calibrated for water level, water temperature, and SS and was validated for the only water level owing to data lack. With the parameters obtained through the appropriate calibration, SS concentrations of inflow into and in the Doam reservoir were simulated for three years (2008, 2004 and 1998) of the minimum, the average, and the maximum of total annual precipitation during recent 30 years. The annual average SS concentrations of the inflow for 2008, 2004, and 1998 were 8.6, 10.9, and 18.4 mg/L, respectively and those in the Doam reservoir were 9.2, 13.8, and 21.5 mg/L. CONCLOUSION(s): The results showed that more intense and frequent precipitation would cause higher SS concentration and longer SS's retention in the reservoir. The HSPF and the CE-QUAL-W2 models could represent reasonably the SS from the Doam watershed and in the Doam reservoir.

Dispersion Characteristics and Mass Transfer in a Pilot‐Scale Gas‐Liquid Oscillatory‐Plate Column

AbstractMass transfer and hydrodynamic characteristics of an oscillatory‐plate column (OPC) and their relation to energy dissipation were investigated using a 0.1‐m diameter pilot‐scale unit. The column is characterized by having plates with a small hole diameter (1.6–3.2 mm) oscillating at 180° out of phase at higher frequencies (0–30 Hz) and small amplitudes (0–3.2 mm). Using this design, it was possible to achieve gas holdup and specific interfacial areas as high as ∼0.8 and 400 m–1, respectively. The maximum gas superficial velocity achieved reaches as high as 1.7 m/s, while the axial dispersion coefficient ranged from ∼10–4 to over ∼3 × 10–3 m2s–1, which is almost one order of magnitude lower than that in bubble columns under similar flow rates. The value of gas velocity of ∼0.1 m s–1 seems to mark a transition beyond which interfacial area, holdup, and axial mixing become practically unchanged. Keeping in view its performance characteristics, the column can satisfactorily meet many of the demands posed by intensified wastewater treatment processes, namely high rates of oxygen transfer, multistage operational mode, uniform distribution of small‐scale turbulence structure, and the ability to handle sludge with relatively high concentrations of suspended solids.

Potentials of anaerobic membrane bioreactors to overcome treatment limitations induced by industrial wastewaters

This review presents a comprehensive summary on applications of anaerobic membrane bioreactor (AnMBR) technology for industrial wastewaters in view of different aspects including treatability and filterability. AnMBRs present an attractive option for the treatment of industrial wastewaters at extreme conditions, such as high salinity, high temperature, high suspended solids concentrations, and toxicity that hamper granulation and retention of biomass or reduce the biological activity. So far, most of the research has been conducted at laboratory scale; however, also a number of full-scale AnMBR systems is currently being operated worldwide. Membrane fouling, a multivariable process, is still a research quest that requires further investigation. In fact, membrane fouling and flux decline present the most important reasons that hamper the wide-spread application of full-scale reactors. This paper addresses a detailed assessment and discussion on treatability and filterability of industrial wastewaters in both lab- and full-scale AnMBR applications, the encountered problems and future opportunities.

The Application of Membrane Contactors for the Removal of Ammonium from Anaerobic Digester Effluent

The present study investigated the removal of ammonia from anaerobic digester effluent using membrane contactors. For mass transfer, hollow fiber membrane contactors offer a multitude of advantages compared to stripping technologies. In conventional applications of membrane contactors, the ammonia rich solution circulates through the fibers. For this kind of application, the very high content of suspended solids in digester effluents requires an additional removal step in order to guarantee undisturbed operation conditions. In a new approach, the membrane fibers were simply submerged into the anaerobic digestate and the performance was investigated at moderate temperatures ranging from 20 to 40°C and pH values lying in the range of 8.6 to 10.0. It was demonstrated that the new approach can be applied efficiently for the treatment of particle rich solutions with high ammonia concentrations of 3.000–3.500 mg/L, obtaining removal rates from 80 up to 98.5%. The mass transfer coefficients lay in the range of 12.4–37.0 × 10−3 m/h and were absolutely comparable to values reported by other authors.

A practitioner’s perspective on the application and research needs of membrane bioreactors for municipal wastewater treatment

The application of membrane bioreactors (MBRs) for municipal wastewater treatment has increased dramatically over the last decade. From a practitioner’s perspective, design practice has evolved over five “generations” in the areas of biological process optimization, separating process design from equipment supply, and reliability/redundancy thereby facilitating “large” MBRs (e.g. 150,000m3/day). MBR advantages and disadvantages, and process design to accommodate biological nutrient removal, high mixed liquor suspended solids concentrations, operation and maintenance, peak flows, and procurement are reviewed from the design practitioner’s perspective. Finally, four knowledge areas are identified as important to practitioners meriting further research and development: (i) membrane design and performance such as improving peak flow characteristics and decreasing operating costs; (ii) process design and performance such as managing the fluid properties of the biological solids, disinfection, and microcontaminant removal; (iii) facility design such as equipment standardization and decreasing mechanical complexity; and (iv) sustainability such as anaerobic MBRs.

Degradation behavior of 17α-ethinylestradiol by ozonation in the synthetic secondary effluent

AbstractEndocrine disrupting chemicals (EDCs) in the secondary effluent discharged from wastewater treatment plants (WWTPs) are of great concern in the process of water reuse. Ozonation has been reported as a powerful oxidation technology to eliminate micropollutants in water treatment. Due to the complexity of the wastewater matrix, orthogonal experiments and single factor experiments were conducted to study the influence of operational parameters on the degradation of 17α-ethinylestradiol (EE2) in the synthetic secondary effluent. The results of the orthogonal experiments indicated that the initial ozone and natural organic matter (NOM) concentration significantly affected EE2 degradation efficiency, which was further validated by the single factor confirmation experiments. EE2 was shown to be effectively degraded by ozonation in the conditions of low pH (6), NOM (10 mg/L), carbonate (50 mg/L), but high suspended solid (20 mg/L) and initial ozone concentration (9 mg/L). The study firstly revealed that the lower pH resulted in higher degradation of EE2 in the synthetic secondary effluent, which differed from EDCs ozonation behavior in pure water. EE2 degradation by ozone molecule instead of hydroxyl radical was proposed to play a key role in the degradation of EDCs by ozonation in the secondary effluent. The ratio between O3 and TOC was identified as an appropriate index to assess the degradation of EE2 by ozonation in the synthetic secondary effluent.

Transparency variation and its influencing factors between different polyculture models with <i>Anodonta woodiana</i> and <i>Hypophthalmichthys molitrix</i>, <i>Aristichthys nobilis</i> in Chinese sturgeon <i>Acipenser sinensis</i> culture pond

中华鲟与背角无齿蚌和鲢鳙混养的池水透明度(SD)对比试验表明,1^#池(对照)、2^#池(挂养背角无齿蚌)、3^#池(混养鲢鳙)透明度平均值分别为11.92、16.45、17.45 cm,分别较试验本底值依次提高26.69%、56.67%、66.19%.2^#、3^#池的透明度显著大于1^#池,最高可达1倍.3个池透明度与各水质指标关系的Panel Data模型分别为:SD₁=-0.0072 TSS+0.8353 NH₄⁺-N-2.1711 TN+0.6195 TP-0.0405 COD+16.7815,SD₂=0.0030 TSS+3.8864 NH₄⁺-N+0.1893 TN-12.4585 TP^***-0.0104 COD+24.5306,SD₃=0.0381 TSS^*+3.7821 NH₄⁺-N+0.6003 TN-15.0444TP^***-0.4078 COD^**+34.2992(*、**、***分别表示显著、较显著、极显著相关).TP是影响中华鲟养殖池透明度的主要指标,NH₄⁺-N、TN、COD是影响透明度的间接指标,而TSS是影响透明度的直接指标.在悬浮物浓度较高、水体浑浊的中华鲟养殖池水体中,鲢鳙的放养对透明度的提高效果显著优于背角无齿蚌.;The results of a transparency (SD) contrast test between different Chinese sturgeon polyculture models with freshwater mussel Anodonta woodiana and silver carp Hypophthalmichthys molitrix, bighead carp Aristichthys nobilis indicated that the average transparencies were 11.92, 16.45, 17.45 cm which increased by 26.69%, 56.67%, 66.19% compared with background value before the test for pond 1 (control group), pond 2 (A. woodiana-polyculture group), pond 3 (H. molitrix, A. nobilis-polyculture group), respectively. The overall transparency level of pond 2 and 3 were significantly higher than that of pond 1, highest reached to twice. The panel data models of three ponds'transparency and other water quality parameters were:SD₁=-0.0072 TSS + 0.8353 NH₄⁺-N-2.1711 TN + 0.6195 TP-0.0405 COD + 16.7815, SD₂=0.0030 TSS + 3.8864 NH₄⁺-N + 0.1893 TN-12.4585 TP^***-0.0104 COD + 24.5306, SD₃=0.0381 TSS^* + 3.7821 NH₄⁺-N + 0.6003 TN-15.0444 TP^***-0.4078 COD^** + 34.2992. Total phosphorus (TP) was the main index, with ammonia nitrogen (NH₄⁺-N), total nitrogen (TN), chemical oxygen demand (COD) as indirect ones, TSS as direct one, influencing the transparency of Chinese sturgeon culture pond. Polyculture with H. molitrix and A. nobilis excels the treatment hanging A. woodiana in transparency rise effects in the Chinese sturgeon culture pond with muddy water and high concentration of total suspended solids.

RO Membrane Filtration of Pretreated Swine Manure with High Levels of Suspended Solids

Sustainable practices require that manure nutrients be reused within the agricultural sector. Reverse osmosis (RO) is one of the few technologies capable of producing nitrogen and potassium concentrates that can be transported to fertilize distant cultivated fields. However, solid-liquid separators produce a liquid fraction that could significantly foul RO membranes because of high colloidal and particulate concentrations. This project investigated the effect of high suspended solids (SS) concentrations, ranging from 258 to 3897 mg L-1, in pretreated manure on the performance of a spiral-wound RO membrane. The effluents were first concentrated to 47% of the initial volume. The concentrates, containing from 453 to 6893 mg SS L-1, were then filtered in full-recycle mode for a total of 22.5 h. Permeate flux stabilized during the full-recycle filtration period at SS levels up to 4000 mg L-1 in RO concentrate, but it was 13% lower at 4016 than at 453 mg SS L-1. At the highest SS level of 6893 mg L-1 in concentrate, flux decreased throughout the full-recycle filtration period, and it was 27% below that measured at 453 mg L-1 after 22.5 h. Lower flux was attributed to the formation of a concentrated gel layer at the membrane surface. While the thickness or density of the gel layer appeared to stabilize below 4000 mg SS L-1 in concentrate, it kept increasing at the highest tested SS level. However, with all effluents, the gel layer was easily removed by rinsing the membrane with tap water, and water flux recovery after rinsing (82.3% 1.6%) and chemical cleaning (99.1% 1.2%) were similar at all SS concentrations. Results thus suggested that spiral-would RO membrane systems could be used to directly process swine manure pretreated by physically based solid-liquid separators, but permeate flux will be significantly reduced at SS concentrations above 4000 mg L-1 in the membrane element.

Structure and dynamics of microbial community in full-scale activated sludge reactors

Phospholipid fatty acid (PLFA) profiles in four full-scale activated sludge reactors (ASR1 ~ 4) treating municipal wastewater, South Korea, were monitored to evaluate the influence of influent water quality on microbial community structure (MCS) and the effect of the MCS on effluent water quality. In ASR1 ~ 3, PLFA profiles were very similar, regardless of the influent water quality and seasonal differences, and 16:17c/15:0iso2OH and 16:0 were dominant. PLFA profiles in ASR4 during summer and autumn were very similar to those in ASR1~3, but increases in specific fatty acids, 16:1ω5c, 11methyl18:1ω7c and 15:0iso3OH, were found in ASR4 during winter and spring, with relatively high total suspended solid (TSS) concentrations in the effluent. 16:1ω5c and 15:0iso3OH, possibly related with Flexibacter sp., caused a bulking problem in the activated sludge. The community diversity indices such as Shannon diversity and equability decreased in summer but increased in autumn in all the ASRs. Canonical correspondence analysis results suggested that the influent BOD concentration played the most important role in changing MCS, followed by influent TSS concentration. In addition, the TSS and total phosphorus concentrations in the effluent were significantly affected by the change of the MCS.

Modeling of the Suspended Solid Concentration of the Jin River Based on High-Spectral Resolution Data

This study used a spectrometer and the above-water sampling method to measure the water's optical properties of the Jin River.The correlation values between high spectral resolution reflectance data and suspended solid concentration(SSC),or between the first derivative of high-resolution reflectance and the SSC showed that the wavelength around 733±3nm was the best one for estimating the SSC of the Jin River.The regression analysis using several regression models revealed that the quadratic polynomial model was the best one to estimate the SSC of the river.It also found that the single-band regression model is more suitable than the first derivative regression model for estimating the SSC of the Jin River.

Application of superconducting HGMS technology on turbid wastewater treatment from converter

Turbid return water from converter is a kind of dust scrubbing wastewater with both high suspended solid concentration and high turbidity, which contains suspended particles such as iron oxide, calcium oxide, silicon oxide, and so on. Usually, it is treated with flocculating sedimentation method, but the addition of flocculant would result in the higher operating cost. In this study, the wastewater from converter was disposed by superconducting high gradient magnetic separation technology. The experimental results showed us that it very useful for both pollutants separation and reuse of wastewater from converter. With the X-ray diffraction analysis, scanning electron microscopy and particles size analysis, the results indicated that not only the ferromagnetic iron oxide, but also weak magnetic substance such as calcium oxide and silica, and nanometer particles could be magnetically coagulated and trapped. Therefore, the suspended solid concentration could be stably controlled as less than 10 mg/L, and the wastewater could be recycled completely at the magnetic field gradient of 3 T. The data reported in this study suggest that the superconducting high gradient magnetic separation technology has a great application prospect: it could be applied without changing the main conventional wastewater treatment process, and it has the advantages of low investment and operating cost, easy and simple handling, and saving water and energy as well.

Integrating satellite imagery and geostatistics of point samples for monitoring spatio-temporal changes of total suspended solids in bay waters: application to Tien Yen Bay (Northern Vietnam)

High concentrations of total suspended solids (TSS) in coastal and bay areas strongly affect water quality and aquatic ecosystems. Frequent monitoring of spatiotemporal changes of TSS distribution in such areas is indispensable for understanding sediment fluxes and water cycles, and to preserve ecosystem health. This study aimed to identify appropriate and sufficient tools for assessing changes in TSS distribution in Tien Yen Bay in Northern Vietnam, a typical closed bay, which was selected as the study area because of its rich biodiversity. Initially, a physical based model using the reflectance at the sea surface was developed for estimating TSS concentrations from satellite image data, and a model with an exponential function was identified as suitable for the estimation. This model was fitted appropriately to provide a relationship between reflectance from the MODIS/Terra band 1 (visible red) after the atmospheric correction and the in situ TSS concentrations at 40 points. Ordinary kriging was then shown to be effective in improving the spatial resolution of the MODIS/Terra image-based estimation of the TSS concentration at a 250 m interval, because it could detect TSS variation in detail, in particular in the local estuaries. TSS distributions derived from 12 MODIS/Terra images from November 2009 to October 2010 clarified seasonal changes in TSS during one year. TSS concentrations were high during summer and lower during fall and winter. Such trends were conformable with the hydrodynamics in Tien Yen Bay. Consequently, the proposed method was more effective for TSS estimation than traditional methods using satellite image data only.

Effects of influent DO/COD ratio on the performance of an anaerobic fluidized bed reactor fed low-strength synthetic wastewater

The effect of influent DO/COD (dissolved oxygen/chemical oxygen demand) ratio on the performance of an anaerobic fluidized bed reactor (AFBR) containing GAC was studied. A high influent DO concentration was found to have adverse impacts on organic removal efficiency, methane production, and effluent suspended solids (SS) concentration. These problems resulted with a DO/COD ratio of 0.12, but not at a lower ratio of 0.05. At first organic removal appeared satisfactory at the higher DO/COD ratio at a hydraulic retention time of 0.30h, but soon a rapid growth of oxygen-consuming zoogloeal-like organisms resulted, eventually causing high effluent SS concentrations. The influent DO also had an inhibitory effect, resulting in a long recovery time for adequate methanogenic activity to return after influent DO removal began. With the growing interest in anaerobic treatment of low COD wastewaters, the increased possibility of similar adverse DO effects occurring needs consideration.

Determination of Chemical Oxygen Demand in Substrates from Anaerobic Treatment of Solid Organic Waste

A modified method is described for the determination of the chemical oxygen demand (COD) of samples with high solids content, especially those used in biogas production. The modified method is based on ISO 6060 and DIN 38414 methods. Analyses with potassium hydrogen phthalate solution standard showed that the modified method is valid and gives equal results to standard method (9,960 mg/L determined by ISO method, and 9,930 mg/L by modified methods). Comparison of the standard method with the new proposed method using actual samples shows that the modified method gives more reliable results than the standard method. The standard ISO 6060 method is more appropriate for samples with homogeneous solids, where uniform dilution is easy to achieve. Although the modified method shows slightly more accurate results, the increased chemical expense associated with the modified method does not justify its use. The proposed modified method is especially appropriate for wet solid samples with high total volatile suspended solids content and the COD values of up to 400,000 mg/kg. COD for waste activated sludge determined by ISO 6060 method was 47,300 and 52,800 mg/kg determined by modified method. COD of original wet solid sample was 360,000 mg/kg, and COD for previously dried samples at 105°C was 345,000 mg/kg. For anaerobically digested sludge the COD was 80,800 mg/kg, and COD for previously dried samples at 105°C was 72,700 mg/kg. The difference is attributed to the loss of volatile compounds in drying. Applying the modified method, samples need no preparation and are analysed in their basic wet form as they are collected from anaerobic digesters. Analysis has shown that currently available methods for COD determination with samples containing high amounts of solids require drying of the sample with the loss of volatile components. This may lead to inaccurate results.

Soil aquifer treatment using advanced primary effluent

Soil aquifer treatment (SAT) using primary effluent (PE) is an attractive option for wastewater treatment and reuse in many developing countries with no or minimal wastewater treatment. One of the main limitations of SAT of PE is rapid clogging of the infiltration basin due to high suspended solid concentrations. Some pre-treatment of PE before infiltration is likely to reduce this limitation, improve performance of SAT and help to implement this technology effectively. The effects of three pre-treatment options namely sedimentation (SED), coagulation (COAG) and horizontal roughing filtration (HRF) on SAT were analyzed by conducting laboratory-scale batch and soil column experiments. The sedimentation and coagulation pre-treatments led to less head loss development and reduction of clogging effect. The head loss development in soil column using PE + COAG and PE + SED was reduced by 85 and 72%, respectively, compared to PE alone without any pretreatment. The overall dissolved organic carbon (DOC) removal of pre-treatments and soil column collectively were 34, 44, 51 and 43.5% for PE without any pre-treatment, PE + SED, PE + COAG and PE + HRF, respectively. Coagulation pre-treatment of PE was found to be the most effective option in terms of suspended solids, DOC and nitrogen removal. Sedimentation pre-treatment of PE could be attractive where land is relatively less expensive for the construction of sedimentation basins.