Retention Of Suspended Solids Research Articles

Investigating the impacts of a recirculation sedimentation application on microalgae biomass cultivation in wastewater treatment

Commercial microalgae production is often interrupted by contamination, leading to short production cycles, reinoculation needs, and culture collapses, significantly increasing costs. This study focuses on investigating Recirculated Sedimentation Application (RSA) to control contamination in microalgae culture systems used for wastewater treatment. Chlorella vulgaris culture was grown in an unsterilized mixture of tertiary treatment effluent and centrate of anaerobic digestion wastewater sludge over a 90-day experimental period. 60 L raceway reactor was operated under a light intensity of 275 μM m−2.s−1 with a 16:8 h light-dark photoperiod. To evaluate the effect of RSA on biological-based problems, the experiment was conducted in three phases. The benefits of utilizing RSA were established through the following observations: effective removal of contaminants at an acceptable level without releasing the culture; extension of the biofilm formation time on the inner walls; inhibition of heterotrophic bacteria and nitrification; enhancement of the suspended solids retention capacity of the raceway tank (up to 770 mg.L−1); and improvement in ammonium removal rate to approximately 30 mg.L−1d−1. The ideal salinity level for both ammonium removal and biomass concentration in RSA should be below 0.02%. These findings demonstrate the potential of phycoremediation for sustainable wastewater treatment and contribute to environmental bioremediation strategies.

Use of Various Thin-Layer Settling Schemes for Industrial Wastewater Treatment

In this paper, the theoretical preconditions in favor of the use of thin-layer settling tanks for industrial wastewater treatment are substantiated by the corresponding laboratory studies. The data from the results of studies of wastewater treatment of the textile, knitwear and silk industries conducted on laboratory thin-layer settling tanks according to the basic schemes of wastewater supply and precipitating sediment are given. As stated by these data, according to the generally accepted criteria for the effectiveness of suspended solids retention for wastewater of the above-mentioned industries, it is more preferable to use thin-layer sedimentation in a cross-sectional scheme.

Hydraulic performance of horizontal constructed wetlands for stormwater treatment: A pilot-scale study in the Mediterranean

Horizontal subsurface flow (HSSF) constructed wetlands (CWs) are widely adopted as a highly effective technique for stormwater treatment. However, the cumulative clogging phenomenon in HSSF is a complex and challenging operative issue affecting removal efficiencies and the lifespan of CWs. This paper aims to evaluate the reliability of a combined approach for assessing the occurrence of clogging and its potential spatial and temporal evolution in two pilot-scale HSSF-CW. The experimental CW system was fed with stormwater runoff from a parking area during the rainy season and sequential batch reactor (SBR) wastewater (WW) during the dry season. The falling head (FH) method and a drainage equation were used to determine the hydraulic conductivity at saturation (Ks) of the porous medium and investigate the hydraulic performance of the system. A residence time distribution (RTD) analysis was also performed to evaluate the hydraulic flow dynamics and define the crucial parameters characterising the CW. The applied hydraulic measurement techniques highlighted that clogging was in the initial stages of development after 2.5 years of operation, likely associated with the presence of a pond and the partial retention of total suspended solids (TSS) by the HSSF system. Overall, the good consistency in the results of the applied methods supports their future application for predicting the occurrence of clogging phenomena in HSSF CWs.

Ultrafiltration for environmental safety in shellfish production: A case of bloom emergence

The process of ultrafiltration (UF) of natural seawater often encounters the problems of variation in water quality and coastal blooms. To validate the feasibility of UF in shellfish farms, this study compared the hydraulic performance and pollutant removal efficiency of the UF process with those of the commonly used treatments that combine several filtration steps with ultraviolet (UV) disinfection. The comparison was conducted in the cases of natural seawater and a coastal bloom. Given that the UF process encountered the specific type of pollution, this study evaluated the filtration performance of the UF process and the retention of total suspended solids (TSS), bacteria, phytoplankton, and zooplankton. A real coastal bloom was considered in the case study of an experimental shellfish hatchery/nursery in France. The results show that both treatments were able to eliminate approximately 50% of TSS. However, in contrast with UV treatment combined with filtration, the UF process retained total amounts of phytoplankton, zooplankton, and bacteria in the bloom. Although the hydraulic performance of the UF process was impacted by the coastal bloom, the fouling was eliminated through chemical cleaning conducted at a frequency less than once per 12 h. Despite the severe pollution, this study confirmed the pollution resistance and treatment performance of the UF process, indicating that UF has the potential to enhance the biosecurity level.

Membrane Bioreactor Technology: The Effect of Membrane Filtration on Biogas Potential of the Excess Sludge.

Although the membrane bioreactor technology is gaining increasing interest because of high efficiency of wastewater treatment and reuse, data on the anaerobic transformations of retentate are scarce and divergent. The effects of transmembrane pressure (TMP) in microfiltration (MF) and ultrafiltration (UF) on the pollutant rejection, susceptibility of ceramic membrane to fouling, hydraulic parameters of membrane module, and biogas productivity of retentate were determined. Irrespective of the membrane cut-off and TMP (0.2–0.4 MPa), 97.4 ± 0.7% of COD (chemical oxygen demand), 89.0 ± 4.1% of total nitrogen, and 61.4 ± 0.5% of total phosphorus were removed from municipal wastewater and the permeates can be reused for irrigation. Despite smaller pore diameter, UF membrane was more hydraulically efficient. MF membrane had 1.4–4.6 times higher filtration resistances than UF membrane. In MF and UF, an increase in TMP resulted in an increase in permeate flux. Despite complete retention of suspended solids, strong shearing forces in the membrane installation changed the kinetics of biogas production from retentate in comparison to the kinetics obtained when excess sludge from a secondary clarifier was anaerobically processed. MF retentates had 1.15 to 1.28 times lower cumulative biogas production than the excess sludge. Processing of MF and UF retentates resulted in about 60% elongation of period in which 90% of the cumulative biogas production was achieved.

Experimental results of the hydrological performance of a permeable pavement laboratory rig

Abstract There is an increasing number of everyday flood incidents around the world, the impact of which poses a challenge to society, the economy and the environment. Under the Water Framework Directive (2000/60/EC), green infrastructure through the use of sustainable drainage systems (SuDS) is the recommended policy to manage and treat storm water runoff. Given the limited published experimental information on permeable interlocking concrete block pavements (PICPs), this paper presents novel results from an experimental laboratory study on a permeable interlocking concrete block pavement rig, investigating the short-term hydrology of the pavement, and water quality aspects related to the retention capacity of suspended solids (SS) through the pavement structure. Results of the volume analysis demonstrate high capability of the permeable structure to reduce the concentration time and attenuate the storm. Water quality testing was employed mainly as an indicator of the tendency of the suspended solids retention by the structure, indicating increasing tendency in the sediment mass retention progressively after each rainfall event. Experimental results obtained in the present study have direct application on the implementation of PICPs in car parking lots, urbanised pavement structures and pedestrianised walkways.

A Highly Efficient Waste-Free Technology of Water and Fuel Preparation for Thermal Power Stations

A highly efficient, economical, and waste-free technology for the purification of natural waters for thermal power plants has been developed. The preliminary purification of water involved microfiltration on tubular ceramic membranes made of clay minerals according to a technology developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; the degree of retention of suspended solids and iron and manganese compounds on the membranes was 99.9, 99.8, and 60%, respectively. The high separation capacity of such membranes is due to the modification of their surface by water contaminants with the formation of a self-organizing dynamic membrane that serves as an additional barrier. The dynamic membrane formation contributed to the retention of up to 24.0% of the co-occurring ions, Ca2+ in particular; this is typical for ultrafiltration membranes. Further desalination was performed with low-pressure reverse osmosis membranes; two stages of reverse osmosis turned out necessary to achieve a total ion content of 0.5 mg/dm3 in the make-up water of a steam turbine unit of a thermal power plant (TPP). The retentate of the second stage of reverse osmosis, for which the total ion content is 50–60 mg/dm3, can be used for technical purposes at TPPs. The salt content of the retentate formed after the first stage of reverse osmosis was ~3 g/dm3, and thus insufficient for further transformation into secondary material resources; however, the introduction of waste recycling systems is considered to be the modern direction in protecting the environment from technological influence. The retentate of the first stage of reverse osmosis was concentrated using an original concentrating electrodialyzer developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; some design modifications that distinguish this electrodialyzer from the conventional ones were proposed and patented. Electrodialysis treatment of the retentate for 2.5 hours at a current density of 2.5 A/dm3 enabled the production of a solution with the ion content of ~105 g/dm3. This brine can be converted into sodium hypochlorite or caustic soda and hydrochloric acid by electrolysis. The diluate with a mineralization of ~200.5 g/dm3 and a total organic carbon content of ~148.3 g/dm3 can be used for the preparation of coal-water slurry fuels for power generation and metallurgy. The basic technological schemes of make-up water purification for the needs of thermal power plants and the preparation of slurry fuel systems based on coal and reverse osmosis waste that contains organic substances are proposed.

The Self-Forming Dynamic Membrane BioReactor (SFD MBR) as a suitable technology for agro-industrial wastewater treatment

Two bench-scale Self-Forming Dynamic Membrane BioReactors (SFD MBR), equipped with 50 μm nylon meshes were set up and operated under aerobic conditions in order to treat canning and winery wastewaters. The results showed different behaviors of the two systems, confirming the strong dependence of SFD MBR performance on the type of biomass and, in turn, on the type of stream being treated. Both plants achieved good results in terms of effluent quality, demonstrating the suitability of the proposed technology. Median values of effluent turbidity were 2.7 and 15.4 NTU (Nephelometric Turbidity Units) in the reactors fed with canning wastewater and winery wastewater, respectively. The removal of organic matter (as COD, Chemical Oxygen Demand) was consistently above 90 %, although the retention of suspended solids was variable and somewhat dependent on operating conditions and feed composition. The activated sludge characteristics were observed to affect filtration performance and in particular the capillary suction time (CST) was a possible indicator of efficiency, with a threshold value of 11 s above which filtration performance decreased. This parameter is proposed as an early warning tool for changes in the filtration performance of an SFD MBR, both for effluent quality and cleaning requirements.

Dynamics of Clay Particles in Non-vegetated Stormwater Biofilters

Stormwater biofilters manage quantity and quality of urban stormwater runoff. Particulate solids from natural and anthropogenic sources accumulate on paved surfaces and eventually reach receiving waters. Retention of suspended solids in stormwater management systems ensures the quality of stormwater runoff to water resources. Stormwater biofilters are similar in most of design parameters to sand filters employed in water treatment systems. The understanding and design of stormwater biofilters are often based on generic models of sand filters. Unlike water treatment sand filters, which are continuously fed, stormwater biofilters operate intermittently with spontaneously alternating wetting and drying cycles. This results in dynamic pollutant removal pattern that employs different mechanisms during and across rainfall events. As such, pilot scale biofilter columns fabricated with a layer of organic material were operated. Removal of suspended solids was very dynamic, where impact of age of filter, antecedent dry days, and inflow quality varied during and across events. Flush of retained solids and filter material occurred during the stabilisation period during each event while very high removal percentages (more than 90%) were observed after stabilisation, during an event. Clogging was not observed due to re-entrainment, re-distribution, and flush of retained solids during intermittent wetting and drying cycles.

Analytical indicators to characterize Particulate Organic Matter (POM) and its evolution in French Vertical Flow Constructed Wetlands (VFCWs)

The design of French VFCWs leads to the formation of a sludge layer at the surface of the first filters due to the retention of suspended solids from the percolation of unsettled wastewater. This layer plays a major role in the system but still little is known on its characteristics and evolutions. In this study, suspended solids and sludge deposits sampled from two French VFCW plants were analyzed by different methods in the objective to assess the evolution of particulate organic matter (POM) along the treatment chain and within the sludge layer, and identify relevant analytical indicators of these phenomena. The treatment chain included an aerobic trickling filter followed by FeCl3 injection and two successive stages of filters.Thermal analyses showed that OM contents of suspended solids decreased along the treatment chain. POM in inflow suspended solids was predominantly composed of reactive, biodegradable compounds which were partly hydrolyzed and mineralized notably at the trickling filter stage. 3D fluorescence spectra collected from aqueous POM extracts confirmed the evolution of organic matter from low-molecular reactive compounds to more complex and stable structures such as humic-like substances. FTIR confirmed the mineralization of POM's reactive constituents along the treatment chain by the decrease in the intensities of the characteristics bands of aliphatic compounds or proteins, and its humification in the sludge deposits through the relative increase of the bands at 1634cm−1 (vC=O) and 1238cm−1 (δC=O and/or δOH). Isotopic ratios δ2H/1H and δ15N/14N were found to be good indicators of POM evolutions. The higher values of δ2H/1H and δ15N/14N ratios measured in sludge deposits as compared to inflow suspended solids were related to POM humification and to microbial processes of POM hydrolysis and mineralization, respectively.

English

The ecosystem services of encroached urban wetlands that receive wastewater and surface run-offs have become more challenging due to climate variability. Our study assessed the seasonal macrophyte diversity and water quality of the streams flowing into and out from Pece wetland in Gulu Municipality. The macrophyte species in the wetland were sampled along five transects. Water samples from the streams were also collected and analyzed in the laboratory. Results indicated forty two macrophyte species that were in twenty four families. Macrophyte diversity and equitability were higher at the wetland edge, but were not significantly different in the entire wetland (p = 0.41, respectively). The recorded faecal coliforms (FC), total suspended solids, electrical conductivity and turbidity in the streams were higher in the wet season than the dry season. The wetland doubled the retention of FC during the dry season and relatively less retention of total suspended solids was recorded in the dry season. The urban expansion and farming might alter the macrophyte abundance and richness in Pece wetland, thus affecting the ecosystem services. Key words: Diversity indices, faecal coliforms, physico-chemical, surface-run-offs, wastewater.

Evaluation of turfgrid porous pavements for urban stormwater management in Xiamen Island, Southeast China

This paper has investigated the runoff retention and pollution removal effectiveness of a frequently used parking area paved with porous turfgrid in Xiamen Island, southeast China. The results have shown that a turfgrid porous paving area of 72 m2 could delay the start time of the runoff generated on it by up to 30 min when rainfall intensity is less than 3.88 mm/h. Although the retention of total suspended solids is only 13.86%, the grass-paved surface can effectively reduce and remove pollutants from the runoff, with the removal of ammonia and NO3 −-N being significant (at 39 and 76.55%, respectively). In addition, high reductions (>60%) in concentration were found for Zn, Cu, and Pb. However, it was found that pollutant concentrations in the infiltration water samples analysed are higher than in the runoff, which suggests the possible occurrence of pollution accumulation as an emerging pollution source. Furthermore, in 2015 no grass was observed in the pores of the pavement, which suggests that a poor maintenance strategy is in place; with this resulting in the development of a potentially high and concentrated source for pollutants.

On-site treatment of used wash-water using biologically activated membrane bioreactors operated at different solids retention times

Biologically activated membrane bioreactors (BAMBis) were operated at suspended solids retention times (SRT) of 7 and 102 days and at full solids retention. The effect of these different approaches of operation on the substrate and nutrient conversion, and on permeate flux, was investigated. Variations in organic loads and aeration intensities were also studied. Permeate flux stabilized during long-term operation independently of suspended SRT. Removal of the organic substrate was independent of solids concentrations and remained stable over the long term. Microorganisms colonizing the surface of particles were found to be the main mechanism responsible for degradation of the organic substrate in the particulate form. BAMBi appeared to be a robust technology, adapted to on-site treatment of used wash-water, as it can be operated without control of suspended SRT. Thus BAMBis can be operated for long periods without any control of biofouling and sludge formation, leading to low maintenance needs. When BAMBis were operated at low aeration, the formation of anoxic zones led to combined nitrification and denitrification and thus significant nitrogen removal.

Simultaneous treatment of raw palm oil mill effluent and biodegradation of palm fiber in a high-rate CSTR

A high-rate continuous stirred tank reactor (CSTR) was used to produce biogas from raw palm oil mill effluent (POME) at 55°C at a highest organic loading rate (OLR) of 19g COD/ld. Physical and chemical pretreatments were not performed on the raw POME. In order to promote retention of suspended solids, the CSTR was installed with a deflector at its upper section. The average methane yield was 0.27l/g COD, and the biogas production rate per reactor volume was 6.23l/ld, and the tCOD removal efficiency was 82%. The hydrolysis rate of cellulose, hemicelluloses and lignin was 6.7, 3.0 and 1.9g/d, respectively. The results of denaturing gradient gel electrophoresis (DGGE) suggested that the dominant hydrolytic bacteria responsible for the biodegradation of the palm fiber and residual oil were Clostridium sp., while the dominant methanogens were Methanothermobacter sp.

Use of vegetated drainage ditches and low-grade weirs for aquaculture effluent mitigation: II. Suspended sediment

Total suspended solids are a priority pollutant under the Clean Water Act and a point of concern for aquaculture facilities. The use of ubiquitous vegetated ditches on the aquaculture landscape may serve as an environmentally and economically sustainable practice for reducing suspended sediment contributions to downstream environments. This study assessed effects of consecutive low-grade weirs on suspended solids retention and settling rates of aquaculture pond effluent in a single drainage ditch. Two control and nine treatment discharges were conducted in September and October 2012 at the Mississippi State University South Farm Aquaculture Facility. All discharges decreased total and volatile suspended solid loads. Total suspended solids were decreased 72–94%, with a significant removal rate of 0.02±0.01mgL−1min−1 in both control (F=6.12, P<0.001) and treatment discharges (F=16.02, P<0.001). Volatile suspended solids comprised 2–80% of total suspended solids and had a significant removal rate of 0.02±0.001mgL−1min−1 in both control (F=10.46, P<0.001) and treatment discharges (F=6.28, P<0.001). There was no significant difference in overall settling rates between control and treatment discharges; however, prior to weir 1, both total and volatile suspended solid concentrations increased in control discharges. Treatment discharges decreased both total and volatile suspended solids significantly (P<0.001) prior to weir 1. Further analysis revealed flow rate to be a significant (P<0.001) variable in total suspended solid removal while initial concentrations affected reduction rates of volatile suspended solids significantly (P<0.001). These results suggest that the use of low-grade weirs could be a viable best management practice that easily integrates within the aquaculture landscape and creates hydraulic conditions conducive to sediment retention.

Removal of particles in organic filters in experimental treatment systems for domestic wastewater and black water

This study assesses the total suspended solids (TSS) retention capacity of different organic filter media for two potential applications: (i) a polishing unit for package treatment plants and (ii) a pretreatment for blackwater from low‐flushing toilets. The results showed that the peat filter media used can be significantly improved in terms of structural stability and TSS removal capacity by mixing it with sawdust. Most of the TSS accumulated in the upper part of the filter material, and filter thickness exceeding 15 cm had no statistically significant effect (P < 0.1) on the TSS treatment performance. The experimental system reached a TSS reduction of 60–70% for blackwater and 80–90% for simulated effluent peaks from a package treatment plant. The main challenge of a full‐scale application of an organic filter is the issue of clogging, especially when treating concentrated blackwater. However, this work indicates that a clogged filter media can be regenerated by mixing the uppermost filter layer without significant loss of filter performance regarding TSS. More research is needed to develop an appropriate mechanical unit for automatic filter media regeneration.

Rethinking the role of in-line coagulation in tertiary membrane filtration of municipal effluents

In-line coagulation with aluminum or iron salts and ultrafiltration (UF) or microfiltration (MF) membranes is a valuable treatment option. The efficiency of the treatment is often evaluated by the achieved separation degree. That separation-oriented approach implies the coagulation with doses that are prohibitively high for many operations including the tertiary effluent treatment. The main purpose of the advanced wastewater treatment however is the retention of microorganisms and suspended solids, and that goal can be achieved even without coagulants. Thus the in-line coagulation can pursue the prevention or minimization of the irreversible fouling as an ultimate goal not related to the maximal separation of organic and inorganic impurities.Pilot experiments at conventional activated sludge (CAS) municipal wastewater treatment plant confirmed that the addition of 1mg/L Fe3+ prevents the irreversible fouling as efficiently as the addition of 5 and 10mg/L Fe3+. The economic impact of the suggested alteration is significant. Estimated operational expenses (OPEX) of a filtration at 60 LMH with 45min cycles and 1 chemical – enhanced backwash per day is around 2cents (€)/m3, almost a half of an OPEX of the separation-oriented treatment.Intermittent in-line coagulation down to first 2.5min of 30 and 45min filtration cycles is another cost-effective method to successfully depress the fouling. The success is explained by two-stage kinetics of a cake formation. At ripening stage, a layer of flocks restricted by a membrane gradually covers its surface and forms an initial dynamic cake. At operable stage, the cake entraps fresh solutes and prevents their contact with a membrane surface even without a coagulant. A superposition of two approaches reduces the consumption of ferric chloride coagulant by 94%.

Surfactants role in the enhancement of the treatment efficiency of the dyeing effluents with combination of membrane processes

The industrial process of reactive dyeing of cotton is a sequence of several operations. Different types of surfactants were used several times during the dyeing process; anionic, nonionic, and cationic. The dyeing effluent is heavily charged with pollution especially color and salt. In a treatment at source approach, the dyeing effluent was isolated and then mixed with the other baths containing surfactants. A combined treatment involving microfiltration (MF), as pretreatment followed by nanofiltration (NF) as mean treatment, was investigated. The mixing of the dyeing bath with another effluent showed 100% of MF flux improvement, but the color retention still higher for the single dyeing bath. The NF treatment produces a completely discolored effluent with 100% of suspended solids retention, while the chlorides removal did not exceed 50%.

Humedal de flujo vertical para tratamiento terciario del efluente físico-químico de una estación depuradora de aguas residuales domésticas

In this study two subsurface vertical flow constructed wetlands were operated and fed with the effluent of physical-chemical process of a municipal wastewater treatment plant, one was planted with the specie Iris pseudacorus (HFV2), and the other one unplanted any kind of vegetation (HFV4). The beds had a depth of 0.80m and were filled with (in cm): 20 coarse-sand, 10 peat moss, 40 fine-gravel and 10 gravel. Three experimental stages were developed with the next hydraulic load (HL): 4.2; 8.3; and 16.6 cm/d (chronological order). The process was evaluated since the steady state was reached. The average removal of COD of the planted wetland with I. pseudacorus was about 81%, whereas into the unplanted substrate was of 68%. This removal of COD was kept constant and was independent of the hydraulic and organic loads. The removal of NH4-N ranged between 75% and 96% in the HFV2, and from 66% to 83% in the HFV4. The high ammonia removal was obtained for the smallest hydraulic load. In the first two phases the performance in removing suspended solids was very low. Most suspended solids removal was observed with maximum hydraulic load that was the last of the series. This suggests that the bed porosity was lost, increasing the efficiency of retention of suspended solids by filtration.

Performance of Hybrid Anaerobic Baffled Reactor in Treating Wastewater with High Strength of Suspended Solids

Operating anaerobic reactors at high strength of suspended solids (SS) can lead to instability and high concentration SS in effluent. To overcome these limitations, anaerobic baffled reactor (ABR) was modified by enlarging the first compartment and filling carriers in up-comer regions to produce the hybrid anaerobic baffled reactor (HABR). Consequently, more favorable conditions were created in the first compartment such as longer hydraulic retention time, better settlement characteristics and longer cell retention time. The carriers improved the retention of SS and cell across the reactor. An ABR with enlarged first compartment (no carriers) was used to compare the performance. The influent COD and SS concentrations were increased from 700 and 300 to 7000 and 2800 mg/L, respectively. After a 187 days operation, with influent COD and SS of 7000 mg/L and 2800 mg/L, both HABR and ABR kept an efficiency of higher than 94.0% in treating COD and an efficiency of higher than 93.0% in removing SS. Higher removals of COD and SS were observed in the HABR than in the ABR. At the same time, performance of HABR was more stable than that of ABR.