Removal Of Particulate Organic Matter Research Articles

Changes in rearing water microbiomes in RAS induced by membrane filtration alters the hindgut microbiomes of Atlantic salmon (Salmo salar) parr

An important step in water treatment in recirculating aquaculture systems (RAS) is the removal of particulate organic matter. While commonly applied treatment technologies remove most of the particles, fine particulate organic matter typically accumulate in RAS, and serve as substrate for heterotrophic bacteria in the system. Membrane ultrafiltration has been shown to reduce the concentrations of total organic carbon and to counteract blooms of opportunistic bacteria in periods with high organic loading. The potential influence of such opportunistic bacteria on the fish microbiomes and fish welfare is poorly understood. In this study, we investigated the effects of high organic loading on the water and hindgut microbiomes in RAS with Atlantic salmon parr. Two pilot-scale RAS, one with membrane ultrafiltration of a 10–15% side-stream (mRAS), and one without (cRAS), were operated in periods with low and high organic loadings, and the water and hindgut microbiomes were characterized by Illumina sequencing of 16S rDNA amplicons. At the end of the experiment, after a period of high organic loading, two OTUs representing Mycobacterium and Spartobacteria dominated the water microbiomes in cRAS, with relative abundances as high as 24 and 17%, respectively. In the mRAS water they were rare (relative abundances of 1.9 and 0.1%). The membrane ultrafiltration stabilized the water microbiota and efficiently prevented the growth of these bacterial populations in RAS. The parr hindgut microbiomes were generally highly distinct from the RAS water microbiomes and were dominated by the bacterial phyla Bacilli and Firmicutes. Furthermore, an OTU probably representing Carnobacterium inhibens, originally isolated from the gut of adult salmon, was highly abundant in the gut microbiomes, with relative abundances reaching over 30%. However, for the cRAS fish after a period with high organic loading, the relative abundance of this Carnobacterium OTU was reduced, and an increased similarity between the gut and the water microbiomes was observed. The Mycobacterium and Spartobacteria OTUs that were abundant in the cRAS water were also abundant in the cRAS hindgut samples. This indicates a direct influence of the water microbiomes on the gut microbiomes, and that high organic loading in the cRAS resulted in growth of opportunistic bacteria that were able to colonize the fish gut. The present study shows that membrane filtration is an applicable strategy to counteract growth of opportunistic bacteria in RAS and to promote positive fish – microbe interactions.

Treatment performance comparison between regular O3\u2013BAC and O3\u2013BAC with rear sand filtration: verification in a full-scale study

BackgroundTo improve the microbial safety of drinking water, an arrangement of O3–BAC with rear sand filtration (O3–BAC–sand) has been proposed. In this study, efforts were devoted to evaluate the benefits and drawbacks of O3–BAC–sand in a full-scale water treatment plant. The performance of the two configurations was compared in terms of particles, turbidity, CODMn and typical odorants and pesticides.ResultsThe O3–BAC–sand yielded lower turbidity but higher CODMn (by approximately 7%) in the finished water than regular O3–BAC (sand–O3–BAC). Both systems removed odors in raw water; however, sand–O3–BAC was more effective on septic and musty odorants. The total pesticide removals by sand–O3–BAC and O3–BAC–sand were 78% and 72%, respectively; though the latter had shorter activated carbon durable years.ConclusionThe re-location of the sand filter would sacrifice the BAC efficiency in removals of organic matter and micropollutants. This tradeoff is a result of the loss of the particulate organic matter removal by sand filters, because locating the sand filter behind BAC causes particle load increase on BAC; some measures of enhanced coagulation should be suggested to improve the turbidity and particle removal. The study will be helpful for improvement of the O3–BAC process in drinking water treatment.

Pilot-scale study to investigate the impact of rotating belt filter upstream of a MBR for nitrogen removal.

The goal of this study was to investigate what kind of impact the removal of particulate organic matter with 33μm rotating belt filter (RBF) (as a primary treatment) will have on the membrane bioreactor (MBR) performance. Two small MBR pilot plants were operated in parallel, where one train treated 2mm screened municipal wastewater (Train A) and the other train treated wastewater that had passed through a RBF with a 33μm filter cloth (Train B). The RBF was operated without a filter mat on the belt. About one third of the organic matter was removed by the fine mesh filter. The assessment of the overall performance showed that the two pilot plants achieved approximately the same removal efficiencies with regard to total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus and total nitrogen. It was also observed that the system with 33μm RBF as a primary treatment produced more sludge, which could be used for biogas production, and required about 30% less aeration downstream. Transmembrane pressure was significantly lower for the train receiving 33μm primary treated wastewater compared to the control receiving 2mm screened wastewater.

Graphene oxide triggers mass transfer limitations on the methanogenic activity of an anaerobic consortium with a particulate substrate

Graphene oxide (GO) is an emerging nanomaterial widely used in many manufacturing applications, which is frequently discharged in many industrial effluents eventually reaching biological wastewater treatment systems (WWTS). Anaerobic WWTS are promising technologies for renewable energy production through biogas generation; however, the effects of GO on anaerobic digestion are poorly understood. Thus, it is of paramount relevance to generate more knowledge on these issues to prevent that anaerobic WWTS lose their effectiveness for the removal of pollutants and for biogas production. The aim of this work was to assess the effects of GO on the methanogenic activity of an anaerobic consortium using a particulate biopolymer (starch) and a readily fermentable soluble substrate (glucose) as electron donors. The obtained results revealed that the methanogenic activity of the anaerobic consortium supplemented with starch decreased up to 23-fold in the presence of GO compared to the control incubated in the absence of GO. In contrast, we observed a modest improvement on methane production (>10% compared to the control lacking GO) using 5 mg of GO L−1 in glucose-amended incubations. The decrease in the methanogenic activity is mainly explained by wrapping of starch granules by GO, which caused mass transfer limitation during the incubation. It is suggested that wrapping is driven by electrostatic interactions between negatively charged oxygenated groups in GO and positively charged hydroxyl groups in starch. These results imply that GO could seriously hamper the removal of particulate organic matter, such as starch, as well as methane production in anaerobic WWTS.

Bioelectrochemical system as an oxidising filter for soluble and particulate organic matter removal from municipal wastewater

A bioelectrochemical system (BES) configuration was designed and tested as a polishing process to remove soluble chemical oxygen demand (SCOD) and suspended solids (SS) from municipal wastewater. The configuration was designed such that the anodic carbon felt could behave as a filter enabling removal and bioelectrochemical oxidation of particulate and soluble organic matter from wastewater. Three reactors (each with approximately 10L liquid volume) were set up to evaluate three different operational settings: (i) close-circuit operation enabling current production; (ii) open-circuit operation without current production; and (iii) control reactor without electrode to account for the effect of electrode as a filter. The reactors were operated for over 200days during which key process parameters (SCOD removal, SS removal, turbidity, electricity production, electrolyte pH) were quantified. The results indicated that current production (maximal current of approximately 120mA) could increase the SCOD removal efficacy from 11% to 77% at a SCOD removal rate of approximately 0.1kgSCOD/m3d. No measurable difference between SS removal efficiencies in open and close circuit (83%), and clogging of the electrode filter were observed. A high coulombic efficiency (more than 80%, based on the SCOD removed) and low internal resistance (2.7Ω) were achieved, indicating that the configuration is suitable for handling real wastewater containing particulate matter. However, active maintenance of a neutral pH at the anode and an acidic cathodic environment (pH<7) were essential to sustain the optimum performance of the system. Overall, this study affirms the potential of using a BES to serve as both a physical filter and an oxidising medium for effluent polishing.

Particulate Organic Matter Affects Soil Nitrogen Mineralization under Two Crop Rotation Systems.

Changes in the quantity and/or quality of soil labile organic matter between and after different types of cultivation system could play a dominant role in soil nitrogen (N) mineralization. The quantity and quality of particulate organic matter (POM) and potentially mineralizable-N (PMN) contents were measured in soils from 16 paired rice-rapeseed (RR)/cotton-rapeseed (CR) rotations sites in Hubei province, central China. Then four paired soils encompassing low (10th percentile), intermediate (25th and 75th percentiles), and high (90th percentile) levels of soil PMN were selected to further study the effects of POM on soil N mineralization by quantifying the net N mineralization in original soils and soils from which POM was removed. Both soil POM carbon (POM-C) and N (POM-N) contents were 45.8% and 55.8% higher under the RR rotation compared to the CR rotation, respectively. The PMN contents were highly correlated with the POM contents. The PMN and microbial biomass N (MBN) contents concurrently and significantly decreased when POM was removed. The reduction rate of PMN was positively correlated with changes in MBN after the removal of POM. The reduction rates of PMN and MBN after POM removal are lower under RR rotations (38.0% and 16.3%, respectively) than CR rotations (45.6% and 19.5%, respectively). Furthermore, infrared spectroscopy indicated that compounds with low-bioavailability accumulated (e.g., aromatic recalcitrant materials) in the soil POM fraction under the RR rotation but not under the CR rotation. The results of the present study demonstrated that POM plays a vital role in soil N mineralization under different rotation systems. The discrepancy between POM content and composition resulting from different crop rotation systems caused differences in N mineralization in soils.

Photochemical production of singlet oxygen from particulate organic matter.

Dissolved organic matter is established as one of the most relevant photosensitizers in aquatic environments, producing singlet oxygen (1O2) alongside other photochemically produced reactive intermediates. While the production of 1O2 from DOM has been well studied, the relative importance of particulate organic matter (POM) to the overall 1O2 production is less well understood. POM is known to play an important role in pollutant fate through the sorption and transport of hydrophobic pollutants. If POM is directly involved in 1O2 production, sorbed molecules would be expected to undergo enhanced photodegradation. In this work, synthetic POM was prepared by coating silica particles with commercial humic acid. The photochemical behavior of these POM samples was compared to dissolved commercial humic acids (DOM). Suspended natural sediment was also studied to test the environmental relevance of the synthetic POM model. Synthetic POM particles appear to simulate well the 1O2-production of suspended sediment. The 1O2 concentrations experienced by POM-sorbed probe molecules was up to 30% higher than experienced by DOM-sorbed ones, even though the aqueous concentration of 1O2 in irradiated POM suspensions was much lower than the analogous DOM solutions. These results were interpreted with a reaction-diffusion model, which suggested that the production rate of 1O2 by POM is lower than DOM, but the loss of 1O2 from the POM-phase is also lower than DOM. Based on the experimental results of this study, calculations were conducted to estimate the impact of removing POM on 1O2-mediated processes. These calculations indicate that compounds with a log Koc value near 4 will be most affected by removal of POM and that the magnitude of the effect is proportional to the fraction of the total organic matter represented by POM. This study demonstrates that particles can play an important role in the degradation of organic compounds via aquatic photochemistry.

Carbon sequestration in clay and silt fractions of Brazilian soils under conventional and no-tillage systems

The capacity of soils to sequestrate carbon (C) is mainly related to the formation of organo-mineral complexes. In this study, we investigated the influence of soil management systems on the C retention capacity of soil with an emphasis on the silt and clay fractions of two subtropical soils with different mineralogy and climate. Samples from a Humic Hapludox and a Rhodic Hapludox, clayey soils cultivated for approximately 30 years under no-tillage (NT) and conventional tillage (CT) were collected from six layers distributed within 100-cm soil depth from each site and from an adjacent native forest. After the removal of particulate organic matter (POM), the suspension (<53 µm) was sonicated, the silt and clay fractions were separated in accordance with Stokes' law and the carbon content of whole soil and physical fractions was determined. In the Humic Hapludox, the clay and silt fractions under NT showed a higher maximum C retention (72 and 52 g kg-1, respectively) in comparison to those under CT (54 and 38 g kg-1, respectively). Moreover, the C concentration increase in both fractions under NT occurred mainly in the topsoil (up to 5 cm). The C retention in physical fractions of Rhodic Hapludox varied from 25 to 32 g kg-1, and no difference was observed whether under an NT or a CT management system. The predominance of goethite and gibbsite in the Humic Hapludox, as well as its exposure to a colder climate, may have contributed to its greater C retention capacity. In addition to the organo-mineral interaction, a mechanism of organic matter self-assemblage, enhanced by longer periods of soil non-disturbance, seems to have contributed to the carbon stabilization in both soils.

Cladoceran Moina branchiata can not reduce suspended solids in Lemna System macrophyte wastewater treatment plant

Mass development of filtering Cladocera in wastewater stabilization ponds is believed to facilitate the removal of particulate organic matter from suspension, thus enhancing the purification efficiency. To evaluate this premise, we monitored the seasonal changes of wastewater characteristics such as suspended solids and chlorophyll a concentration, pH, oxygen concentration and biological oxygen demand (BOD), and population density of the cladoceran Moina branchiata in the 3.5m deep ponds of two Lemna System plants, differing in the degree of surface cover by Lemna minor. We found no detectable effect of M. branchiata on any of the above parameters, despite its occasionally very high population densities (over 2000 ind.L−1). We conclude that cladoceran grazing is negligible in organic particle removal from wastewater passing deep Lemna ponds that are heavily loaded with dissolved and particulate organic matter.

Decadal cycling within long-lived carbon pools revealed by dual isotopic analysis of mineral-associated soil organic matter

Long-lived soil organic matter (SOM) pools are critical for the global carbon (C) cycle, but challenges in isolating such pools have inhibited understanding of their dynamics. We physically isolated particulate (>53 μm), silt-, and clay-sized organic matter from soils collected over two decades from a perennial C3 grassland established on long-term agricultural soil with a predominantly C4 isotopic signature. Silt- and clay-sized fractions were then subjected to a sequential chemical fractionation (acid hydrolysis followed by peroxide oxidation) to isolate long-lived C pools. We quantified 14C and the natural 13C isotopic label in the resulting fractions to identify and evaluate pools responsible for long-lived SOM. After removal of particulate organic matter (~14% of bulk soil C) sequential chemical treatment removed 80% of mineral-associated C. In all mineral-associated fractions, at least 55% of C4-derived C was retained 32 years after the switch to C3 inputs. However, C3–C increased substantially beginning ~25 years after the switch. Radiocarbon-based turnover times ranged from roughly 1200–3000 years for chemically resistant mineral-associated pools, although some pools turned over faster under C3 grassland than in a reference agricultural field, indicating that new material had entered some pools as early as 14 years after the vegetation switch. These findings provide further evidence that SOM chemistry does not always reflect SOM longevity and resistance to microbial decomposition. Even measureable SOM fractions that have extremely long mean turnover times (>1500 years) can have a substantial component that is dynamic over much shorter timescales.

Dynamics and elemental stoichiometry of carbon, nitrogen, and phosphorus in particulate and dissolved organic pools during a phytoplankton bloom induced by in situ iron enrichment in the western subarctic Pacific (SEEDS-II)

The dynamics of organic carbon (C), nitrogen (N), and phosphorus (P) were examined during an in situ mesoscale iron-enrichment experiment in the western North Pacific in the summer of 2004. We separately determined the production of particulate organic matter (POM) and dissolved organic matter (DOM) and their subsequent removal during the bloom decline. As the iron-induced phytoplankton bloom progressed (days 0–14), POM increased in the surface mixed layer, while DOM did not increase significantly. The molar ratios for C:N, C:P, and N:P of the newly produced POM were estimated to be 4.9, 190, and 37 in the surface mixed layer, whereas the dissolved inorganic nitrogen to soluble reactive phosphorus drawdown ratio was 17. Preferential remineralization of P over C and N from the POM was postulated during the developing phytoplankton bloom. During the bloom decline (days 16–25), surface POM decreased with a similar C:N of 5.2. The N:P ratio of surface DOM increased during the bloom decline. Below the surface mixed layer, DOC and DON increased moderately after the peak of the bloom. The time-series variation of DOC and DON was not identical. The C, N, and P dynamics through the accumulation and removal of POM and DOM were complex. Grazing by mesozooplankton during the experiment may have played a significant role in the uncoupling of the dynamics of C, N, and P.