Low Suspended Solids Concentrations Research Articles

Separation of Short-Chain Fatty Acids from Primary Sludge into a Particle-Free Permeate by Coupling Chamber Filter-Press and Cross-Flow Microfiltration: Optimization, Semi-Continuous Operation, and Evaluation.

Short-chain fatty acids (SCFAs) are valuable metabolic intermediates that are produced during dark fermentation of sludge, which, when capitalized on, can be used as chemical precursors for biotechnological applications. However, high concentrations of solids with SCFAs in hydrolyzed sludge can be highly detrimental to downstream recovery processes. This pilot-scale study addresses this limitation and explores the recovery of SCFAs from primary sludge into a particle-free permeate through a combination of chamber filter-press (material: polyester; mesh size: 100 µm) and cross-flow microfiltration (material: α-Al2O3; pore size: 0.2 µm; cross-flow velocity: 3 m∙s-1; pressure = 2.2 bars). Firstly, primary sludge underwent dark fermentation yielding a hydrolyzate with a significant concentration of SCFAs along with total solids (TS) concentration in the range of 20 to 30 g∙L-1. The hydrolyzate was conditioned with hydroxypropyl trimethyl ammonium starch (HPAS), and then dewatered using a filter press, reducing TS by at least 60%, resulting in a filtrate with a suspended solids concentration ranging from 100 to 1300 mg∙L-1. Despite the lower suspended solids concentration, the microfiltration membrane underwent severe fouling due to HPAS's electrostatic interaction. Two methods were optimized for microfiltration: (1) increased backwashing frequency to sustain a permeate flux of 20 L∙m-2∙h-1 (LMH), and (2) surface charge modification to maintain the flux between 70 and 80 LMH. With backwashing, microfiltration can filter around 900 L∙meff-2 (without chemical cleaning), with the flux between 50 and 60 LMH under semi-continuous operation. Evaluating the particle-free permeate obtained from the treatment chain, around 4 gCSCFAs∙capita-1∙d-1 can be recovered from primary sludge with a purity of 0.85 to 0.97 CSCFAs∙DOC-1.

Why the disinfection efficiency of ultraviolet radiation may become unsatisfactory at low suspended solid concentrations: The mechanism of extracellular polymeric substances secretion induced by different particles.

Due to the global outbreaks caused by pathogens, disinfection has attracted widespread attention, especially as the final inactivation step in wastewater treatment plants (WWTPs). Ultraviolet (UV) radiation is regarded as one of low carbon disinfection methods without chemical agents, but in practice, the effects are sometimes unsatisfactory, e.g., Escherichia coli (E. coli) still stay alive excessively at low concentrations of suspended solids (SS) that meets the discharge standards (<10 mg l-1). WWTPs focus on each process's efficiency, while the particle influence of different upstream processes on UV radiation is ignored. This study investigated the changes in extracellular polymeric substances (EPS) structure and biofilm from the perspective of single cell and cell-to-cell interactions at low SS concentrations before and after UV radiation. We disclosed that the effective characteristics of effluent SS particles were mainly related to some specific operation units, like coagulation sedimentation or sand filtration, which induced EPS secretion and biofilm formation, and subsequently caused the different responses of cells within the biofilm to UV radiation. Compared with filtrating sand particles, the magnetic coagulant induced more polysaccharide secretion and expanded the EPS structure, leading to a thicker and more effective protective layer to weaken UV intensity and reduce reactive oxygen species levels inside cells. The microbial community analysis of a real WWTP confirmed the survival of microorganisms with abilities of EPS secretion and sheltering others. Therefore, considering the potential positive effect of particles (such as metal particles) in the upstream process on the microbial aggregation in the subsequent process, it is recommended that the UV disinfection requires a lower SS concentration standard or a higher UV radiation dose. This study provides a basis for effective UV disinfection at the present application standards.

Pattern-based assessment of the influence of rainfall characteristics on urban stormwater quality.

Urbanisation increases pollutant generation within catchments and their transport to receiving waters. Changes to rainfall patterns, particularly in the age of climate change, make pollution mitigation a challenging task. Understanding how rainfall characteristics could influence the changes to stormwater pollutant runoff is important for designing effective mitigation strategies. This study employed a pattern-based assessment of relationships between rainfall characteristics and stormwater quality in urban catchments to develop this understanding. The research outcomes showed that rainfall events could be distinctly clustered based on intensity and duration, and each cluster of events would produce different stormwater quality responses. The high-intensity bursts occurring in the latter part of long-duration events were found to produce uniform and low concentrations of suspended solids. One the contrary, high intensity bursts occurring in the initial part of short-duration events triggered the first-flush effect, thus producing high concentrations of suspended solids. Furthermore, the first-flush effect was likely to present when the high intensity bursts occurred in the mid portion of rainfall events and produced variable concentrations of suspended solids. It was also found that the average rainfall intensity plays a key role in mobilising and transporting pollutants accumulated on urban surfaces.

Influence Of Activated Carbon On Total Suspended Solids And Relative Plugging Index Of Injection Water From X-Oilfield

Produced water will be used as injection water for water flooding need, but, based on the results of water quality tests show poor injection water quality caused by a lot of solids particles with high total suspended solids (TSS) concentration and high relative plugging index (RPI) obtained in the injection water. When, the condition of injection water without treatment is injected into formation will cause serious plugging. In this study, two methods used to minimize the high TSS and RPI problems are treatment with chemical and filtration (activated carbon). The use of optimal concentration of scale inhibitor in the injection water can reduce TSS and RPI in the injection water, but it does not work effectively, so that its water quality is still poor water quality and can cause plugging in the formation. Another method is filtration with activated carbon filter media which has characteristics of adsorption and large specific area to filter insoluble materials in the injection water. After filtration, the filtrate of the injection water results in clear water condition. Based on the results of laboratory tests indicate that the filtrate of the injection water contains the least solids particles with small particle size, low total suspended solids concentration and low relative plugging index value. When, it is injected into formation, the possibility of plugging occurrence can be minimized, although, there is increase of pH value, but, in general, the filtrate of the injection water can be categorized good water quality

Color profile and microstructure of the nacre shell of an invasive freshwater mussel, Sinanodonta woodiana, at different elevations in West Java, Indonesia

The Chinese pond mussel Sinanodonta woodiana is an invasive freshwater mussel in Indonesia but has economic potential owing to the production of hemispherical pearls in their nacreous shell. To our knowledge, this study is the first to report on the species' shell nacre color profile and correlate it with microstructure and environmental factors at different elevations, from sea level to more than 1500 m. Samples from Lowland, Midland, and Highland elevations in West Java Province were observed and analyzed using the scanning electron microscope for shell microstructure. In addition, the nacre color was analyzed using spectrophotometry and estimated using the CIE Yxy color space and yellowness index. The nacre color ranged from gold to yellow and silvery. The microstructure at five positions on the shell was observed with a scanning electron microscope. The nacre with gold color had a thicker whole nacre layer, thinner nacre tablet thickness, and narrower surface nacre tablet area. In contrast, the nacre with silver color had a thinner whole nacre layer, thicker nacre tablet thickness, and greater surface nacre tablet area. The posterior position of shell nacre had a strong gold color with a high yellowness index, whereas the anterior and dorsal positions had a yellow color, and the central and ventral positions had a silver color. Mussels from the Midland locations displayed strong gold-colored nacre with a high yellowness index and high brightness. Based on these results, Midland areas are considered to have optimum environmental conditions for hemispherical pearl culture. S. woodiana shell with a thicker nacre layer and thinner nacre tablet shows a strong gold color, whereas a thinner nacre layer and thicker tablet nacre has a silvery color. We surmise that environments with high chlorophyll-a concentrations and low concentrations of total suspended solids result in the thicker nacre layer and the stronger gold color in the inner shell of S. woodiana.

Effects of suspended solids on cyanobacterial bloom formation under different wind fields.

Wind waves and suspended solids (SS) generated by the resuspension of sediments are ubiquitous characteristics of lake ecosystems. However, their effects on phytoplankton remain poorly elucidated in shallow eutrophic lakes. Laboratory experiments were carried out to investigate the responses of Microcystis aeruginosa to SS under static (wind speed of 0m/s) and breeze (wind speed of 3m/s) conditions. Results showed that 50mg/L SS can promote the growth of M. aeruginosa, accelerate the formation of colonies, and increase the floating rate under no-wind conditions. Comparing with static environment, breeze can significantly increase the growth rate of M. aeruginosa and benefit the formation of larger colonies of algae cells. Driven by wind and SS, the buoyancy of the cyanobacteria community in different experimental groups was obviously different. The specific performance was that low SS concentration and breeze were in favor of the floating of cyanobacteria, while high SS concentration went against the floating of algal cells. As a conclusion, wind speed of 3m/s and 20-50mg/L SS have a synergistic effect on the formation of cyanobacterial blooms. This study can provide an improved current understanding of bloom formation and turbidity management strategies in shallow eutrophic lakes.

Impact of different inoculum sources on the performance of membrane bioreactors for municipal wastewater treatment: Dynamic membrane versus ultrafiltration membrane

In this study, impact of different inoculum on the performance of membrane bioreactors (MBRs) was investigated for municipal wastewater treatment. Waste sludges from a conventional activated sludge (CAS) system and a high-rate activated sludge (HRAS) system were used as inoculums at Stage-1 and Stage-2, respectively. A commercial ultrafiltration (UF) membrane was tested in parallel with a low-cost polyester hollow fiber support material (dynamic membrane, DM). UF and DM membranes were operated for 67 days at a flux of 8 L/m2·h at each stage. High chemical oxygen demand (COD) and soluble COD (sCOD) removal efficiencies (>86% and >74%, respectively), low mixed liquor suspended solids (MLSS) concentration (<10 mg/L), and low turbidity values were achieved in permeates at each stage. Extracellular polymeric substances (EPS) content was higher at Stage-1, which caused an increase in sludge resistance to filtration (SRF) and sludge volume index (SVI). Based on morphological analysis, compact dynamic cake layer was formed on the support material at Stage-1, while porous dynamic layer was formed at Stage-2. Thus, DM was operated at lower TMP at Stage-2. Based on the results obtained from the study, sludge from HRAS system showed better performance as inoculum compared to the sludge from CAS system for DM applications.

Water-quality and ecosystem impacts of recreation in streams: Monitoring and management

There is limited published information on the impact of bathing on stream water quality and ecology, except on human pathogens and health. We investigated the relationships between environmental quality of streams and recreational activity at five sites in the Australian Wet Tropics. The streams normally had very low concentrations of nutrients and suspended solids (TSS), but concentrations fluctuated widely during spates, thereby causing difficulties in discriminating impacts. Daily bathing activity disturbed sediments causing an increase in TSS and turbidity, which greatly exceeded national guidelines for maintenance of aesthetic qualities. TSS returned to background levels overnight as bathing areas were flushed clean. Total nitrogen and phosphate concentrations also increased with bather numbers, and phosphate concentrations were directly proportional to bather density. Faecal coliform concentrations were elevated by bathers at one site. Ecological effects of bathers were equivocal and greater on algal than invertebrate assemblages. Water quality degradation, although transient, suggested that some sites were close to their carrying capacity for bathers. Our results show that water quality may vary with local conditions and that cost-effective monitoring and management require development of cause-effect models of water quality processes for each stream site.

Enhancing the performance of thermophilic anaerobic digestion of food waste by introducing a hybrid anaerobic membrane bioreactor

The thermophilic anaerobic digestion of food waste was a long-term challenge for maintaining process stability. A hybrid submerged anaerobic membrane bioreactor (AnMBR), integrating 27%(v/v) polyurethane sponge as fixed carriers were therefore investigated at (50 ± 2) °C. The organics removal efficiencies, COD mass balance, and membrane filtration performance were investigated in a 75-days continuously operated experiment. The results showed that methane production reached 0.31 L/(kg·COD) under an organic loading rate of 7.3 kg·COD/(m3·d). The low concentration of total volatile fatty acids of 247 ~ 274 mg/L and a high proportion of Methanosarcina (>97%) represented the high stability of the thermophilic process. Approximately 21% of biomass grew on the carriers in the hybrid AnMBR and induced a much lower suspended solids concentration and viscosity of bulk sludge. Noticeable lower trans-membrane pressure was consequently observed. The affecting factors identified by PCA analysis proved the advantages of the hybrid AnMBR for alleviating membrane fouling formation.

Coupled effects of bacteria and suspended solids on clogging during managed aquifer recharge

Managed aquifer recharge (MAR) is an effective strategy for relieving water shortages and their related environmental problems. However, clogging is a major issue in MAR implementation. Bioclogging occurs when nutrients and suspended solids (SS) are available in the water to which bacteria can be attached and subsequently form larger aggregations that result in porous media clogging. The combined clogging of SS and Pseudomonas aeruginosa (P.a) bacteria was investigated using a series column experiment, and scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), correlation analysis, and pathway analysis were employed to identify the combined clogging interaction between SS and P.a. Low SS concentrations exhibited high mobility and improved the migration of P.a as carriers, while high SS concentrations promoted the deposition of P.a. Thus, SS changed the stage characteristics of bioclogging, and the order of the clogging rate was as follows: SS–P.a group > P.a group > SS group. The interaction mechanisms of the combined clogging included bridging ions, chemical bonds, functional groups, extracellular polymeric substance polymerization, and improved adhesion within the SS–P.a sand system, which formed polymers with large particle sizes that occupied the pores and narrowed the flow path, causing the media to clog. The correlation and pathway analyses demonstrated that the direct effect of biomass was larger than SS on combined clogging, but the indirect effects of biomass were less than those of the SS, indicating that a series of interactions occurred during the SS–P.a combined clogging, and more special attention should be paid to the interaction of SS and bacteria during the aquifer recharge process.

A Comparative Study of a Moving Bed Biofilm Reactor and Bio-shaft Technology for a Wastewater Treatment Process: A review

In addition to the primary treatment, biological treatment is used to reduce inorganic and organic components in the wastewater. The separation of biomass from treated wastewater is usually important to meet the effluent disposal requirements, so the MBBR system has been one of the most important modern technologies that use plastic tankers to transport biomass with wastewater, which works in pure biofilm, at low concentrations of suspended solids. However, biological treatment has been developed using the active sludge mixing process with MBBR. Turbo4bio was established as a sustainable and cost-effective solution for wastewater treatment plants in the early 1990s and ran on minimal sludge, and is easy to maintain. This has now evolved into a technology that has proven successful worldwide with trouble-free operation and improved Turbo4bio technology, an advanced high-intensity ventilation system fully enclosed and non-mechanical, ensuring odor-free operation, simple and environmentally friendly operation and long life of domestic and commercial wastewater treatment And the municipality. In this paper, a comparison between MBBR and T4B treatment system was made. As a general review of previous research and experiments, it is possible to reduce the total cost based on building all plant structures to obtain concentrations within the permissible limits of pollutants at the final outlets. It is clear that the use of MBBR has contributed to the realization of simultaneous biological phosphorous and nitrogen removal experiments, which aim to change the more significant methods developed from conventional methods, from the advantages of the Turbo 4 Bioreactor with low cost and high production performance, with less energy consumption and lower operating costs because it does not require Chemicals for processing, cleaning, and disinfection. It only takes small amounts of chlorine, the use of a compressor system for air, and rapid recovery providing high rates of generation of biomass to restore the plant quickly.

Dynamic membrane bioreactor performance for treatment of municipal wastewaters at different sludge concentrations

In this study, the effect of sludge concentration on the performance of an aerobic dynamic membrane bioreactor (DMBR) was investigated. Low-cost polyester hollow fiber support material was used for the formation of dynamic membrane (DM). Treatment and filtration performances of the DMBR were investigated at two different sludge concentrations (5 g/L; 10 g/L). Both DMBRs were operated at a flux of 18 L/m 2 h The DM could be operated at steady conditions for 51 and 24 days at sludge concentrations of 5 and 10 g/L, respectively. High treatment performance and permeate quality were achieved at each sludge concentration. High chemical oxygen demand (COD) removal (>88%), low total suspended solids (TSS) concentrations (<10 mg/L), and low turbidity values (<1.15 NTU) were achieved by both DMs. However, a shift to a relatively larger range in particle size distribution of permeate were observed at high sludge concentration. Furthermore, higher transmembrane pressure was observed at the sludge concentration of 10 g/L, resulting in a rapid clogging. At the tested conditions, overall results indicated that selection of the optimum sludge concentration played a significant role in achieving homogeneous and stable DM layer in DMBRs. • Hollow fiber support materials made of polyester were used for dynamic membrane formation. • DMBR performances were investigated at two different sludge concentrations (5 and 10 g/L). • Almost similar treatment performances were obtained with both membranes. • A rapid membrane clogging was observed at the high sludge concentration.

A Novel Procedure of Total Organic Carbon Analysis for Water Samples Containing Suspended Solids with Alkaline Extraction and Homogeneity Evaluation by Turbidity.

This study was conducted to develop and validate a more reliable total organic carbon (TOC) analytical procedure for water samples containing suspended solids (SS). The effects of the combined ultrasonic and alkaline pretreatment (CULA) on the TOC measurement were studied in water samples containing SS from three origins (algae, sewage particles, and soil) under different analytical conditions (SS concentration, oxidation methods, and sieve size). The applicability of turbidity as a homogeneity index was also evaluated. With CULA, TOC recovery remained high (>80%) for SS concentration ranges up to four times larger than ultrasonic pretreatment alone (UL) due to enhanced particulate organic carbon (POC) solubilization, and did not significantly differ depending on the oxidation methods, at low SS concentrations, or with varying sieve sizes. In particular, the turbidity change rate (i.e., NTU5/NTU0) of the pretreated water sample showed a high correlation with TOC precision (r2 = 0.73, p < 0.01), which suggests that turbidity can be used as an indicator of sample homogeneity. A novel TOC analytical procedure is expected to be useful for more accurate assessments of the impact of particulate pollutants on water quality than current methods, and for the analysis of the carbon cycle, including POCs, in the environment.

Evaluation of moving bed sand filter for denitrification, suspended solids removal and very low effluent total phosphorus concentrations.

Continuously flushing moving bed sand filter was operated in pilot scale for phosphorus (P) and nitrogen removal with simultaneous particle removal. The wastewater tested was either final effluent from a municipal wastewater treatment plant (WWTP) with nitrogen removal in moving bed biofilm reactors (MBBRs) followed by coagulation and dissolved air flotation (DAF) for P and suspended solids (SS) removal, or different mixtures of this final effluent and effluent from the MBBR-stage. The study focused on the applicability to achieve low total phosphorus (TP) concentrations (below 0.1 mg/L) and suspended solids concentrations (below 10 mg SS/L), plus good denitrification (removal rate over 750 g NO3-N/m3-d), by treating wastewater having variable concentrations of TP (from 0.19 to 7.3 mg/L), SS (from 3 to 169 mg/L) and total nitrogen (from 8 to 27 mg/L). The target effluent TP limit was easily achieved when adding coagulant to WWTP effluent. With correct coagulant dose (Al/TP-molar ratio >4) and good particle removal the target effluent TP could also be reached when treating mixed WW with fairly high influent TP. Very high denitrification rates were achieved with adequate influent P concentration and external carbon source. Low denitrification rates were observed when limited by low concentrations of biodegradable carbon and phosphorus.

Determining factors for the occurrence and richness of submerged macrophytes in major Korean rivers

The natural flow regime in Korean rivers is approaching that of a lentic environment, and submerged macrophytes have become widely distributed throughout the river systems. To manage river ecosystems, it is important to identify the key environmental factors that affect species occurrence and richness of submerged macrophytes. Here, we examined the environmental factors that affect species occurrence and richness of submerged macrophytes after the major rivers project in Korea. We collected data for species presence/absence and species richness from 197 surveyed sites (from 2014 to 2015) along the five major rivers in Korea. Water environmental variables were obtained from the Ministry of Environment’s national water quality measurement network (from January 2012 to October 2015). We used a boosted regression model and generalized additive model to identify the crucial water environmental factors related to occurrence and diversity of submerged macrophytes. The boosted regression model indicated that submerged macrophytes were abundant in waters with low concentrations of suspended solids and chlorophyll a. The generalized additive model showed that suspended solids, chlorophyll a, and water current velocity had the greatest effects on species richness, which declined with increasing water turbidity and flow velocity. Our results confirm observations in other impacted river systems and ask for a better understanding of the underlying environmental factors affecting macrophytes abundance and species richness.

Replenishment of landscape water with reclaimed water: Optimization of supply scheme using transparency as an indicator

With shortages of urban water resources, reclaimed water (RW) has become increasingly important as an alternative water source, especially for replenishing landscape waters. To meet the requirements of landscape quality control when RW is used for partial replacement of the surface water (SW) source to a channel-type urban water in a city in northwest China, scenario analyses were carried out by mathematical modelling. Water transparency (measured by SD) is used as an intuitive indicator to reflect the comprehensive influence of suspended solids (SS) and algae growth on the water’s aesthetic quality. Findings indicate that although the significantly higher nutrient concentrations of RW might bring about higher algae growth potential, in comparison with SW, its much lower SS concentration could offset the adverse effects on SD, to a large extent. By embedding the water quality model, calibrated and validated based on a two-year measurement data into MIKE 3 software for both SD and algae growth calculation, computer simulations were carried out to assist a series of scenario analyses of RW utilization and optimization of the water supply scheme. As a result, to meet the requirement of SD > 80 cm at the control section of the landscape water, the total water inflow required was not increased but decreased with the optimal application of RW. The advantages of lower SS in RW to reduce the demand inflow of total water was more evident with the higher requirement of SD. Replenishment of the channel-type urban water by RW was, thus, proven feasible from the viewpoint of landscape quality control.

Wpływ pokrycia dachu na ilość i wielkość zawiesin w spływach deszczowych

Among various drainage surfaces which allow rainwater to be utilised locally, roofs are frequently chosen solution. This is because they represent a big share of all sealed surfaces in cities and discharged liquids are considered potentially clean. Scientific reports confirm that pollutants accumulate on roofs and influence the quality of discharged water. Suspended solids are the biggest group of pollutants which occur in runoffs. The selection of rainwater pre-treatment installation and further use of the water depends on the concentration of suspended solids and their particle size. This article describes results of a research concerning suspended solids discharged from roofs made of traditional materials as well as green-roofs located in urban areas. The quantity and size of particles were assessed against rainfall characteristics: rainfall depth, length of antecedent dry weather periods and season. Results of the research show diversity of concentration levels and size of suspended solids within runoffs in reference to roofing materials, rainfall characteristics and season. The highest concentrations of suspended solids in runoff from traditional roofs were observed during rainfall depth less than 5 mm, after ancedent dry weather periods more than 50 h and in winter. These parameters did not have significantly influence on the low concentrations of suspended solids in runoff from green roofs. Suspended solids particles with the size of up to 200 μm constitute the biggest share of all roof runoffs.

Ecology of duckweed ponds used for nutrient recovery from wastewater.

The microorganism community that grows under duckweed shelter can play an important role on treatment processes. Therefore, the present study aimed to assess the zooplankton dynamic and microbial community in duckweed ponds (DPs) applied for domestic wastewater treatment under open field conditions. A pilot system comprised of two DPs in series (DP1 and DP2), with 10 m2 each, received domestic wastewater through a flow rate of 200 L·day-1. Thus, the system was monitored during 314 days through samples collected and analysed weekly. Also, the zooplankton organisms were identified and quantified. DNA sequencing was performed in order to identify the bacterial populations. The findings showed a high efficiency of nutrient removal with 93% and 91% of total phosphorus and total nitrogen, respectively. A high density of microcrustaceans was observed in DP1 reaching 4,700 org.100 mL-1 and rotifers (over than 32,000 org.100 mL-1) in DP2, that could be related to the low suspended solids concentration (<30 mg·L-1) and turbidity (<10 NTU). The bacterial community showed a strong heterogeneity between samples collected along the seasons. Through these findings, it is possible to realise that the understanding of ecology could help to enhance the operation and designs of DPs.

Microalgae-bacteria aggregates: effect of the hydraulic retention time on the municipal wastewater treatment, biomass settleability and methane potential

BACKGROUND The use of microalgae–bacteria systems is particularly attractive for wastewater treatment, and the generated biomass can be further used for methane production. The aim of this study was to evaluate the influence of the hydraulic retention time (HRT) on the organic matter, nutrient removal, settling properties and the biochemical methane potential using a granular microalgae–bacteria system in a high rate algal pond. RESULTS The primary microorganisms present in the system were constituted by diatoms, green filamentous microalgae and bacteria. At 2 d of HRT the system showed the lowest performance while high chemical oxygen demand (COD) (>92%), ammonium (>85%) and phosphorus (up to 30%) removal was observed at 6 and 10 d of HRT. High settling velocities (up to 8 m h−1) were observed due to agglomerates and granules as dominant structures. The highest methane yield and production rates (348 mL CH4 g−1 VS and 56 mL CH4 g−1 VS d−1) were observed with the biomass obtained at 10 d of HRT. CONCLUSION Flocs and granules were the dominant structures in the system. High settling velocities and low effluent total suspended solids concentrations were obtained at higher HRT. An inverse relationship between HRT and the biochemical methane potential was observed. © 2016 Society of Chemical Industry

The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations.

Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, K D. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in K D were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the K D (n = 15 for each metal, p > 0.05) for Mn (r 2 = 0.0063), Cu (r 2 = 0.0002, Cr (r 2 = 0.021), Ni (r 2 = 0.0023), Cd (r 2 = 0.00001), Co (r 2 = 0.096), Hg (r 2 = 0.116) or Pb (r 2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of K D. The findings conform to the increasingly documented theory that the use of K D in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 μg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water.