Aerobic Degradation Of Organic Matter Research Articles

Organic Matter Removal Performance of Enhanced Sewer Self-purification by Porous Media Treating Domestic Wastewater under Various Temperatures

The organic matter removal performance of a channel for enhanced sewer self-purification by porous media was investigated. The effect of temperature, within a range of about 10 to 28°C, on aerobic organic matter degradation was focused on, using real domestic wastewater as influent. A channel was observed for 96 days between the months of October to December, via a mass balance approach. Mass balance analysis revealed that organic matter removal mostly occurred via oxidation and that organic matter retention inside the channel was minimal. Using the oxygen consumption rate as a measure of organic matter removal, the evaluated removal performance was between 6.4–33.4 g O2 m−2 d−1 expressed per area of porous sponge media. Oxygen consumption rates were observed to increase with increased temperature of the porous sponge media and was not affected by fluctuations in organic loading. The results highlighted that enhanced sewer self-purification by porous media is anticipated to perform well in regions with average temperatures above 20°C.

“Cattle dung biochar-packed vertical flow constructed wetland for nutrient removal”: Effect of intermittent aeration and wastewater COD/N loads on the removal process

The effect of varying COD/N ratio (1:1, 3:1, 5:1, 8:1, 10:1) of wastewater and intermittent aeration on treatment efficiency of biochar (BC)-packed (with 10% V/V biochar) vertical flow constructed wetland (VFCW), planted with Colocasia esculenta was assessed in this study. Three setups of VFCW were prepared in two sets: aerated (with an airflow rate of 1.0 ± 0.6 L min−1 for 6 h d−1) and non-aeration, and changes in COD, NH4+-N, NO3-N, TN, and TP (total phosphorous) in the effluent was investigated. In VFCWS with intermittent aeration, COD, NH4+-N, NO3-N, TP removal was 99.0, 97.0, 81.0, and 89.0%, significantly higher (p < 0.05) than non-aerated VFCW setups as 91.3, 70.9, 86.97 and 64.4%, respectively. In non-aerated VFCWs, BC addition in combination with plantation was advantageous in the nutrient removal process than setups without BC. COD/N ratio of wastewater did not show a significant impact on the working of VFCWs if amended with BC and intermittent aerations, suggesting slow adsorption rate and fast aerobic degradation of organic matter. The study suggests that oxygen supply management and BC addition in VFCWs could be an effective strategy to treat wastewater with a high organic load. Apart from that study results will be useful for refinement of the operational strategy with varying organic load.

Performance of Biodrying Process based on Temperature Profile and Cumulation

The biodrying process of solid waste is an approach to the use of biomass energy, where solid waste is dried using the heat generated from aerobic degradation of organic matter. Temperature profile and cumulation of the solid waste biodrying process are the success factors in drying solid waste. The reactor used is made of plywood with dimensions of (30 × 30 × 100) cm equipped with a heat sink using Thermoshield Universal to minimize heat loss. Aeration discharge at the biodrying process reactor is 0.023 m3/kg/h. The results showed a maximum temperature of 61°C produced from the bottom layer of the biodrying reactor (addition of 6 l / min air flow) on the first day at 10:00 pm. Cumulation temperature in the bottom layer of the biodrying reactor for 21 days of research reached 186.9°C. This value is a source of heat generated from the decomposition of waste under aerobic conditions. Based on the three layers, it can be concluded that the bottom layer produces higher temperature cumulation than the top or middle layer. This research can be a reference for determining temperature monitoring points and knowing Temperature cumulation generated from the waste decomposition process using biodrying technology.

The impact of intertidal areas on the carbonate system of the southern North Sea

Abstract. The coastal ocean is strongly affected by ocean acidification because of its shallow water depths, low volume, and the closeness to terrestrial dynamics. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea, a northwest European shelf sea, revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent back-barrier tidal areas (Wadden Sea) in summertime is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea tidal basins and the North Sea and the consequences for the carbonate system in the German Bight are estimated using a 3D ecosystem model. The aim of this study is to differentiate the various sources contributing to observed high summer TA in the southern North Sea. Measured TA and DIC in the Wadden Sea are considered as model boundary conditions. This procedure acknowledges the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. According to the modelling results, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is less than a previous estimate but within a comparable range. The interannual variabilities in TA and DIC, mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Dynamics in the carbonate system are found to be related to specific weather conditions. The results suggest that the Wadden Sea is an important driver for the carbonate system in the southern North Sea. On average 41 % of TA inventory changes in the German Bight were caused by riverine input, 37 % by net transport from adjacent North Sea sectors, 16 % by Wadden Sea export, and 6 % were caused by internal net production of TA. The dominant role of river input for the TA inventory disappears when focusing on TA concentration changes due to the corresponding freshwater fluxes diluting the marine TA concentrations. The ratio of exported TA versus DIC reflects the dominant underlying biogeochemical processes in the Wadden Sea. Whereas aerobic degradation of organic matter played a key role in the North Frisian Wadden Sea during all seasons of the year, anaerobic degradation of organic matter dominated in the East Frisian Wadden Sea. Despite the scarcity of high-resolution field data, it is shown that anaerobic degradation in the Wadden Sea is one of the main contributors of elevated summer TA values in the southern North Sea.

Aquifer heat storage: abundance and diversity of the microbial community with acetate at increased temperatures

The temperature affects the availability of organic carbon and terminal electron acceptors (TEA) as well as the microbial community composition of the subsurface. To investigate the impact of thermal energy storage on the indigenous microbial communities and the fluid geochemistry, lignite aquifer sediments were flowed through with acetate-enriched water at temperatures of 10, 25, 40, and 70 °C in sediment column experiments. Genetic fingerprinting revealed significant differences in the microbial community compositions with respect to the different temperatures. The highest bacterial diversity was found at 70 °C. Carbon and TEA mass balances showed that the aerobic degradation of organic matter and sulfate reduction were the primary processes that occurred in all the columns, whereas methanogenesis only played a major role at 25 °C. The methanogenic activity corresponded to the highest abundance of an acetoclastic Methanosaeta concilii-like archaeon and the most efficient degradation of acetate. This study suggests a significant impact of geothermal energy storage on the natural microbial community and various metabolic activities because of increased temperatures in sediments with a temperature-related sediment organic matter release.

Sludge Bio-drying Process at Low Ambient Temperature: Effect of Bulking Agent Particle Size and Controlled Temperature

Sludge bio-drying is an aeration process for the removal of water. The drying process utilizes the bio-heat generated from aerobic degradation of organic matter in sludge. In this study, four trials were run in the winter season at ambient temperatures of between 3°C and 9°C. The physical and chemical changes that occurred during the process were investigated and the impacts of the particle sizes of bulking agents and the controlled-matrix temperature were assessed. Results indicated that the process can start up in winter with a three-day lag, while the total duration was only seven days. The highest water removal rate (of 31.0%) with the least organic matter loss (of 12.2%) was obtained at a lower controlled matrix temperature (of 43°C) with a bulking agent of mixed particle size. As a common bulking agent, straw, which has a small particle size of 2–5 mm, was beneficial for organic matter degradation, while it had a negative effect on water removal. The use of different types of straw (with larger particle size of 20–30 mm) as the bulking agent gave poor performance, in which the organic matter degradation rate was 9.75% and the water removal rate was 25.9%. Higher controlled temperature (53°C) resulted in less aeration but degradation rates were enhanced to 16.8%. The using of lower temperatures (43°C) resulted in lower water removal rate (of 29.2%) and relatively lower biodegradation rate.

Tracing organic compounds in aerobically altered methane-derived carbonate pipes (Gulf of Cadiz, SW Iberia)

The primary geochemical process at methane seeps is anaerobic oxidation of methane (AOM), performed by methanotrophic archaea and sulfate-reducing bacteria (SRB). The molecular fingerprints (biomarkers) of these chemosynthetic microorganisms can be preserved in carbonates formed through AOM. However, thermal maturity and aerobic degradation can change the original preserved compounds, making it difficult to establish the relation between AOM and carbonate precipitation. Here we report a study of amino acid and lipid abundances in carbonate matrices of aerobically altered pipes recovered from the seafloor of the Gulf of Cadiz (SW Iberian Peninsula). This area is characterized by a complex tectonic regime that supports numerous cold seeps. Studies so far have not determined whether the precipitation of carbonate pipes in the Gulf of Cadiz is a purely chemical process or whether microbial communities are involved. Samples from this site show signs of exposure to oxygenated waters and of aerobic alteration, such as oxidation of authigenic iron sulfides. In addition, the degradation index, calculated from the relative abundance of preserved amino acids, indicates aerobic degradation of organic matter. Although crocetane was the only lipid identified from methanotrophic archaea, the organic compounds detected (n-alkanes, regular isoprenoids and alcohols) are compatible with an origin from AOM coupled with bacterial sulfate reduction (BSR) and subsequent aerobic degradation. We establish a relation among AOM, BSR and pipe formation in the Gulf of Cadiz through three types of analysis: (1) stable carbon and oxygen isotopic composition of carbonate minerals; (2) carbonate microfabrics; and (3) mineralogical composition. Our results suggest that carbonate pipes may form through a process similar to the precipitation of vast amounts of carbonate pavements often found at cold seeps. Our approach suggests that some organic compound patterns, in combination with additional evidence of AOM and BSR, may help indicate the source of altered methane-derived carbonates commonly occurring in ancient and modern deposits.

Sedimentary phosphorus dynamics and the evolution of bottom‐water hypoxia: A coupled benthic–pelagic model of a coastal system

The present study examines oxygen and phosphorus dynamics at a seasonally hypoxic site in the Arkona basin of the Baltic Sea. A coupled benthic–pelagic reactive‐transport model is used to describe the evolution of bottom‐water solute concentrations, as well as pore‐water and sediment profiles. Aerobic respiration dominates remineralization, with iron reduction, denitrification, and sulphate reduction playing secondary roles, while other pathways are negligible. Sediments represent a significant oxygen sink chiefly due to the aerobic degradation of organic matter, as well as nitrification and iron oxyhydroxide precipitation. Most phosphorus deposited in sediments is in organic matter, yet cycling is dominated by iron‐bound phosphorus due to rapid dissimilatory iron reduction coupled with aerobic iron oxyhydroxide formation. Sustained hypoxia results in an initial decrease in sediment phosphorus content due to dissolution of phosphorus‐bearing iron oxyhydroxides, resulting in a pulse of phosphate to overlying waters. Although an organic‐rich layer is formed under low‐oxygen conditions, enhanced remineralization of organic phosphorus relative to organic carbon tempers sedimentary phosphorus accumulation. Upon reoxygenation of bottom waters after a decade of sustained hypoxia, oxygen concentrations do not immediately achieve values observed prior to hypoxia because the organic‐rich layer creates a higher benthic oxygen demand. Artificial reoxygenation of bottom waters leads to a substantial increase in the iron‐bound phosphorus pool; the total phosphorus content of the sediment, however, is unaffected. A relapse into hypoxia would consequently produce a large pulse of phosphate to the overlying waters potentially exacerbating the situation.

Sediment profile imaging (SPI) and micro-electrode technologies in impact assessment studies: Example from two fjords in Southern Chile used for fish farming

Two state-of-the-art techniques were used to assess the impact of organic loading from fish farming in two fjords of Southern Chile, Pillan and Reñihue Fjords. A sediment profile imaging (SPI) camera was deployed and sediment microprofiles (oxygen, H 2S, redox and pH) were measured in undisturbed sediment cores collected using a HAPS corer. Four out of seven stations in Pillan Fjord were found to be severely disturbed: SPI images showed azoic conditions (no apparent Redox Potential Discontinuity layer, no evidence of aerobic life form, presence of an uneaten fish food layer, negative OSI scores). These findings were corroborated by very high oxygen consumption rates (700–1200 mmol m − 2 day − 1 ), H 2S concentrations increasing quickly within the sediment column and redox potential decreasing towards negative values within a few mm down core. Results for Reñihue Fjord were not so straightforward. SPI images indicated that most of the stations (R3 to R7) presented well-mixed conditions (high apparent RPD layers, presence of infauna, burrows, etc.), but oxygen profiles yielded consumption rates of 230 to 490 mmol m − 2 day − 1 and organic carbon mineralization of 2.16 to 4.53 g C m − 2 day − 1 . These latter values were close to the limit of aerobic degradation of organic matter although no visible changes were recorded within the sediment column. In view of our findings, the importance of integrating multidisciplinary methodologies in impact assessment studies was discussed.

Links of organic carbon cycling and burial to depositional depth gradients and establishment of a snowball Earth at 2.3Ga. Evidence from the Timeball Hill Formation,Transvaal Supergroup, South Africa.

Closely spaced samples of carbonaceous shales and siltstones from two upwards coarsening deltaic parasequences of the early Paleoproterozoic Timeball Hill Formation of the Pretoria Group, Transvaal Supergroup were analysed for their organic carbon content and isotopic composition. We illustrate that trends in the organic carbon isotopic signature are closely linked to changes in the depositional environment and also to variations in climate. Systematic trends displayed by organic carbon isotope values suggest that a biosynthetic chain transporting organic carbon from the oxygen-rich surface water to anoxic deep water was already present in the early Paleoproterozoic Ocean. Just as in modern deltaic environments, aerobic degradation of organic matter occurred in the shallow water and recycling of organic matter in the deeper water led to the preservation of isotopically light organic carbon. Sampling in a sequence stratigraphic framework also reveals that over time, the preserved organic matter became more13C enriched. This trend may be linked to a global decrease in atmospheric CO2 which eventually led to a major ice-age that is recorded by glacial diamictite capping the Timeball Hill Formation. The results confirm that in order to reach a better understanding of organic carbon cycling in the Precambrian, sedimentary facies, depositional environment and post-depositional modifications of carbon isotopic values must be taken into account.

Induction of denitrification in a pilot-scale trickling filter by adding nitrate at high loading rate

Oxygen transferred from the liquid phase into a biofilm can be used for aerobic degradation of organic matter and for nitrification. A second possible pathway for the removal of organic matter is denitrification in anoxic zones deeper in the biofilm. At high organic loading rates with insufficient oxygen supply to the biofilm, denitrification could be induced by providing the biofilm with external nitrate. This possibility was tested in a pilot-scale trickling filter by adding a pulse of nitrate to a highly loaded trickling filter. The experiment showed that denitrification can indeed be induced by adding nitrate at high loading conditions and that this way a considerably increased substrate removal capacity can be obtained. The fact that denitrification occurred was confirmed by the increased production of CO2 from bioconversion processes, without a major change of the O2 consumption. The simplified mixed-culture biofilm model developed by Rauch et al. was extended for the description of off-gas measurements and was able to describe the results of the experiment very well.

Early diagenesis of organic matter from sediments of the eastern subtropical Atlantic: evidence from stable nitrogen and carbon isotopes

Stable isotopes of sedimentary nitrogen and organic carbon are widely used as proxy variables for biogeochemical parameters and processes in the water column. In order to investigate alterations of the primary isotopic signal by sedimentary diagenetic processes, we determined concentrations and isotopic compositions of inorganic nitrogen (IN), organic nitrogen (ON), total nitrogen (TN), and total organic carbon (TOC) on one short core recovered from sediments of the eastern subtropical Atlantic, between the Canary Islands and the Moroccan coast. Changes with depth in concentration and isotopic composition of the different fractions were related to early diagenetic conditions indicated by pore water concentrations of oxygen, nitrate, and ammonium. Additionally, the nature of the organic matter was investigated by Rock-Eval pyrolysis and microscopic analysis. A decrease in ON during aerobic organic matter degradation is accompanied by an increase of the 15N/ 14N ratio. Changes in the isotopic composition of ON can be described by Rayleigh fractionation kinetics which are probably related to microbial metabolism. The influence of IN depleted in 15N on the bulk sedimentary (TN) isotope signal increases due to organic matter degradation, compensating partly the isotopic changes in ON. In anoxic sediments, fixation of ammonium between clay lattices results in a decrease of stable nitrogen isotope ratio of IN and TN. Changes in the carbon isotopic composition of TOC have to be explained by Rayleigh fractionation in combination with different remineralization kinetics of organic compounds with different isotopic composition. We have found no evidence for preferential preservation of terrestrial organic carbon. Instead, both TOC and refractory organic carbon are dominated by marine organic matter. Refractory organic carbon is depleted in 13C compared to TOC.

The fate of carbon in continental shelf sediments of eastern Canada: a case study

This paper discusses the effects of organic carbon oxidation on the dissolution and precipitation of calcium carbonate (aragonite and calcite) in fine-grained continental shelf and slope sediments, using data obtained during the Canadian Joint Global Ocean Flux Study program in the Gulf of St. Lawrence and on the Scotia shelf. The oxygen-penetration depth in these sediments is on the order of 10–15 mm, indicating that organic carbon is mineralized aerobically within this interval. Below this depth, organic matter degradation proceeds mostly through anoxic mineralization processes. The organic carbon content of these sediments decreases smoothly with depth. At all sites, the bottom water is supersaturated with respect to calcite. However, in most cores, immediately below the sediment–water interface, the acidity produced by the aerobic degradation of organic matter is sufficient to overcome the supersaturation of the overlying waters and induce CaCO 3 dissolution. This is most strongly reflected by an increase in the porewater calcium concentration near the sediment–water interface. Deeper in the cores, the saturation state of the porewaters increases at depth as a result of alkalinity generation by sulfate reduction and CaCO 3 of precipitates. Unlike organic carbon, the inorganic carbon content of the sediments therefore varies little or even increases with depth because what is lost through dissolution near the sediment–water interface is replaced at depth by precipitation. The carbon precipitated as CaCO 3 in the sulfate-reduction zone originates in part from the organic carbon, resulting in the preservation of a fraction of the original organic carbon as inorganic carbon. The precipitation of CaCO 3 in the anoxic zone creates an additional source of CO 2 to the porewaters. The geochemical significance of this source is discussed.

Modeling of aerobic biodegradation and oxygen consumption in benthic sediments

A brief overview of the existing chemical and biological models of biodegradation in porous media is given. A revised biological model of aerobic degradation of organic matter in benthic sediments is developed. The model is based on steady state balance equations for microbial mass, organic matter, and oxygen. The biomass balance equation involves a logistic trophic function (instead of the classical Malthusian one) describing the self‐regulation of microbial abundance. One of the corollaries of the model is the dependence of the decay rate upon the organic matter content S in the form dS/dt ∝ S2/(S + Ks)2 (where Ks is a constant) that implies two extreme cases: dS/dt is independent of S at small Ks (refractory organics) and dS/dt ∝S2 at large Ks (labile organics), instead of the commonly used law dS/dt ∝ S. The oxygen consumption rate J is expressed through the oxygen concentration O0 in the overlying water and three generalized parameters. This function demonstrates the effect of the plateau at large O0. The dependence J(O0) is calibrated for the three experimental systems of the literature, two of which have high oxygen consumption rates and one low. For the latter, the model parameters are estimated and their correspondence to the evidence available is discussed. Depth profiles of oxygen, organic matter, and biomass are computed and the aerobic zone thickness is determined.

Changes in the isotopic and chemical composition of ground water resulting from a recharge pulse from a sinking stream

The Little River, an ephemeral stream that drains a watershed of approximately 88km2 in northern Florida, disappears into a series of sinkholes along the Cody Scarp and flows directly into the carbonate Upper Floridan aquifer, the source of water supply in northern Florida. The changes in the geochemistry of ground water caused by a major recharge pulse from the sinking stream were investigated using chemical and isotopic tracers and mass-balance modeling techniques. Nine monitoring wells were installed open to the uppermost part of the aquifer in areas near the sinks where numerous subterranean karst solution features were identified using ground penetrating radar. During high-flow conditions in the Little River, the chemistry of water in some of the monitoring wells changed, reflecting the mixing of river water with ground water. Rapid recharge of river water into some parts of the aquifer during high-flow conditions was indicated by enriched values of delta 18O and delta deuterium (−1.67 to −3.17per mil and −9.2 to −15.6per mil, respectively), elevated concentrations of tannic acid, higher (more radiogenic) 87Sr/86Sr ratios, and lower concentrations of 222Rn, silica, and alkalinity compared to low-flow conditions. The proportion of river water that mixed with ground water ranged from 0.10 to 0.67 based on binary mixing models using the tracers 18O, deuterium, tannic acid, silica, 222Rn, and 87Sr/86Sr. On the basis of mass-balance modeling during steady-state flow conditions, the dominant processes controlling carbon cycling in ground water are the dissolution of calcite and dolomite in aquifer material, and aerobic degradation of organic matter.

Use of Chemical and Isotopic Tracers to Characterize the Interactions Between Ground Water and Surface Water in Mantled Karst

AbstractIn the mantled karst terrane of northern Florida, the water quality of the Upper Floridan aquifer is influenced by the degree of connectivity between the aquifer and the surface. Chemical and isotopic analyses [18O/16O (δ18O), 2H/1H (δD), 13C/12C (δ13C), tritium (3H), and strontium‐87/strontium‐86 (87Sr/86Sr)] along with geochemical mass‐balance modeling were used to identify the dominant hydrochemical processes that control the composition of ground water as it evolves downgradient in two systems. In one system, surface water enters the Upper Floridan aquifer through a sinkhole located in the Northern Highlands physiographic unit. In the other system, surface water enters the aquifer through a sinkhole lake (Lake Bradford) in the Woodville Karst Plain. Differences in the composition of water isotopes (δ18O and &lt;δD) in rainfall, ground water, and surface water were used to develop mixing models of surface water (leakage of water to the Upper Floridan aquifer from a sinkhole lake and a sinkhole) and ground water. Using mass‐balance calculations, based on differences in δ18O and δD, the proportion of lake water that mixed with meteoric water ranged from 7 to 86% in water from wells located in close proximity to Lake Bradford. In deeper parts of the Upper Floridan aquifer, water enriched in 18O and D from five of 12 sampled municipal wells indicated that recharge from a sinkhole (1 to 24%) and surface water with an evaporated isotopic signature (2 to 32%) was mixing with ground water.The solute isotopes, δ13C and 87Sr/86Sr, were used to test the sensitivity of binary and ternary mixing models, and to estimate the amount of mass transfer of carbon and other dissolved species in geochemical reactions. In ground water downgradient from Lake Bradford, the dominant processes controlling carbon cycling in ground water were dissolution of carbonate minerals, aerobic degradation of organic matter, and hydrolysis of silicate minerals. In the deeper parts of the Upper Floridan aquifer, the major processes controlling the concentrations of major dissolved species included dissolution of calcite and dolomite, and degradation of organic matter under oxic conditions. The Upper Floridan aquifer is highly susceptible to contamination from activities at the land surface in the Tallahassee area. The presence of post‐ 1950s concentrations of 3H in ground water from depths greater than 100 m below land surface indicates that water throughout much of the Upper Floridan aquifer has been recharged during the last 40 years. Even though mixing is likely between ground water and surface water in many parts of the study area, the Upper Floridan aquifer produces good quality water, which due to dilution effects shows little if any impact from trace elements or nutrients that are present in surface waters.

Do macrophytes play a role in constructed treatment wetlands?

The larger aquatic plants growing in wetlands are usually called macrophytes. These include aquatic vascular plants, aquatic mosses and some larger algae. The presence or absence of aquatic macrophytes is one of the characteristics used to define wetlands, and as such macrophytes are an indispensable component of these ecosystems. As the most important removal processes in constructed treatment wetlands are based on physical and microbial processes, the role of the macrophytes in these has been questioned. This paper summarizes how macrophytes influence the treatment processes in wetlands. The most important functions of the macrophytes in relation to the treatment of wastewater are the physical effects the presence of the plants gives rise to. The macrophytes stabilise the surface of the beds, provide good conditions for physical filtration, prevent vertical flow systems from clogging, insulate the surface against frost during winter, and provide a huge surface area for attached microbial growth. Contrary to earlier belief, the growth of macrophytes does not increase the hydraulic conductivity of the substrate in soil-based subsurface flow constructed wetlands. The metabolism of the macrophytes affects the treatment processes to different extents depending on the type of the constructed wetland. Plant uptake of nutrients is only of quantitative importance in low-loaded systems (surface flow systems). Macrophyte mediated transfer of oxygen to the rhizosphere by leakage from roots increases aerobic degradation of organic matter and nitrification. The macrophytes have additional site-specific values by providing habitat for wildlife and making wastewater treatment systems aesthetically pleasing.

Einfluß von LAS auf den Bioabbau organischer Substanzen/ Effect of LAS (Linear Alkylbenzene Sulphonates) on organic matter biodegradation

LAS (linear alkylbenzene sulphonates) are still the main surfactants used in formulated detergent products and are an important component of urban sewage. Surfactants could be toxic for microorganisms responsible for the degradation treatment and to organisms present in natural ecosystems. However sewage treatment plants are not designed to eliminate surfactants. It is interesting therefore to study the effect of LAS on microorganisms in microbiological treatment units to determine the residual LAS concentration reaching the collector channels This article discusses the effect of LAS on the purification efficiency of aerobic sewage treatment plants, and LAS biodegradation itself in such plants. The results of this study suggest that LAS influence pH self-regulation capacity in aerobic degradation of organic matter when its concentration is greater than 20 ppm. For this, external neutralisation is required in such cases. Likewise, LAS influence the degradation capacity of both organic matter and itself in aerobic processes, reducing the biodegradation rate and increasing the residual COD and LAS concentrations obtained.

Sediment biogeochemistry in an East African mangrove forest (Gazi Bay, Kenya)

The biogeochemistry of mangrove sediments was investigated in several mangrove forest communities in Gazi Bay, a coastal lagoon in Kenya, Africa. Carbon dioxide fluxes, sediment median grain sizes, sedimentary organic carbon, nitrogen and phosphorus contents and pore-water characteristics (ammonium, nitrate, sulfate and chloride) could be related to forest type. Mangrove sediments have pH values that range from 3.5 to 8.3 due to the limited buffer capacity of these sediments and intense acidifying processes such as aerobic degradation of organic matter, oxidation of reduced components, ammonium uptake by roots and root respiration. The mangrove sediments are nitrogen-rich compared to mangrove litter, as a result of microbial nitrogen retention, uptake and fixation, and import of nitrogen-rich material. It appears that mangrove sediments in Gazi Bay act as a nutrient and carbon sink rather than as a source for adjacent seagrass and reef ecosystems.

Diel Pulses of O_2 and CO_2 in Sandy Lake Sediments Inhabited by Lobelia Dortmanna

Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation on sandy sediments in nutrient—poor softwater lakes in North America and Europe. We report here the discovery of pronounced depth profiles and pulses of dissolved O2 and CO2 in the pore—water of vegetated sediments between light and darkness. Pulses of O2 and CO2 were extensive in the upper sediment layers of high root density, because Lobelia roots absorb CO2 and release O2 during photosynthesis but absorb O2 and release CO2 during respiration, whereas fluxes across leaf surfaces are impeded by a cuticle of low gas permeability. Release of most O2 from the roots during Lobelia photosynthesis leads to O2 concentrations close to saturation in the root zone and O2 penetration to great sediment depth because of low microbial O2 consumption rates. The CO2 concentrations in the root zone of the most nutrient—poor sediments examined here (0.37—0.71 mmol/L) were below the levels required to saturate Lobelia photosynthesis (&gt;3 mmol/L), and experimental enrichment with CO2 stimulated the development of higher O2 concentrations in the root zone. Cycles of O2, CO2 and nutrients are, therefore, intimately coupled in the Lobelia—sediment system, in contrast to terrestrial and other aquatic plants, where gas and nutrient fluxes are physically separated between leaves and roots and their respective surrounding media. The release of O2 from the roots should ensure efficient aerobic degradation or organic matter, lead to oxidized forms of Fe, Mn, and N, and can supply O2 to mycorrhizal fungi and an aerobic fauna associated with the roots.