Biological Oxidation Of Organic Matter Research Articles

Bioelectrochemical technology for recovery of silver from contaminated aqueous solution: a review.

A large amount of silver-rich wastewater is generated from different industrial processes. This wastewater is not considered a waste, but a valuable source for recovery due to the precious silver (Ag). Previous studies have used traditional methods such as membrane filtration, electrolysis, chemical precipitation, electrochemical, and cementation for Ag recovery. However, many drawbacks have been reported for these techniques such as high cost, hazardous waste generation, and the needed refinement of recovered products. In this study, a bioelectrochemical system (BES) for Ag recovery from aqueous solution is introduced as an effective and innovative method, as compared with other techniques. Different types of Ag(I)-containing solutions that have been investigated in recent BES studies (e.g., Ag+ solution, [Ag(NH3)2]+, [Ag(S2O3)]-, [Ag(S2O3)2]3- complexes) are reported. A BES is an anaerobic system consisting of anode and cathode chambers, which are normally separated by an ion-exchange membrane. The electron flow obtained from the anodic biological oxidation of organic matter is used directly for the cathodic electrochemical reduction of Ag(I) ions. The recovered product is Ag electrodeposits, formed at the cathode surface. Several studies have reported high Ag recovery efficiency by using a BES (i.e., > 90%), with high purity of metallic silver, and simultaneous electricity production. Furthermore, a BES can be employed for a wide range of initial Ag(I) concentrations (e.g., 50-3000mg/L). The advantages of BES technology for Ag recovery are highlighted in this study for further practical applications.

Vertical and horizontal distribution of fluorescent dissolved organic matter in the Southern Ocean

The vertical and horizontal distribution of fluorescent dissolved organic matter (FDOM), determined by fluorescence intensity at 320 nm excitation and 420 nm emission, were clarified in nine stations on two transects at the Southern Ocean, including a subtropical, subantarctic, polar frontal and Antarctic zone. All vertical profiles of fluorescence intensity showed that levels were lowest in the surface waters, increased with increasing the depth in mid-depth waters (∼ 2000 m), and then stayed within a relatively narrow range from there to the bottom. Such vertical profiles of FDOM were similar to those of nutrients, but were adverse to dissolved oxygen. In water columns below the temperature-minimum subsurface water (dichothermal waters) in the Antarctic zone and below the winter mixed layer in the other zones, we determined the relationships of fluorescence intensity to concentrations of nutrients and apparent oxygen utilization (AOU) over the entire area of the present study, and found significant linear correlations between the levels of fluorescence intensity and nutrient concentrations ( r = 0.70 and 0.71 for phosphate and nitrate + nitrite, respectively) and AOU ( r = 0.91). From the strong correlation coefficient between fluorescence intensity and AOU, we concluded that FDOM in the Southern Ocean is formed in situ via the biological oxidation of organic matter. The regeneration of the nutrients/consumption of the oxygen/formation of FDOM was active in mid-depth waters. However, the correlations between fluorescence intensities and nutrients and AOU were different in the mid-depth water masses, Subantarctic Mode Water (SAMW), and Antarctic Intermediate Water (AAIW), indicating that the sources of organic matter responsible for FDOM formation were different. A considerable amount of FDOM in the SAMW is thought to be produced by the remineralization of DOM in addition to sinking particulate organic matter, while DOM is less responsible for FDOM formation in the AAIW.

Biogeochemical transformations of arsenic in circumneutral freshwater sediments.

Arsenic is a wide-spread contaminant of soils and sediments, and many watersheds worldwide regularly experience severe arsenic loading. While the toxicity of arsenic to plants and animals is well recognized, the geochemical and biological transformations that alter its bioavailability in the environment are multifaceted and remain poorly understood. This communication provides a brief overview of our current understanding of the biogeochemistry of arsenic in circumneutral freshwater sediments, placing special emphasis on microbial transformations. Arsenic can reside in a number of oxidation states and complex ions. The common inorganic aqueous species at circumneutral pH are the negatively charged arsenates (H2As(V)O4(-) and Has(V)O4(2-)) and zero-charged arsenite (H3As(III)O3(0)). Arsenic undergoes diagenesis in response to both physical and biogeochemical processes. It accumulates in oxic sediments by adsorption on and/or co-precipitation with hydrous iron and manganese oxides. Burial of such sediments in anoxic/suboxic environments favors their reduction, releasing Fe(II), Mn(II) and associated adsorbed/coprecipitated As. Upward advection can translocate these cations and As into the overlying oxic zone where they may reprecipitate. Alternatively, As may be repartitioned to the sulfidic phase, forming precipitates such as arsenopyrite and orpiment. Soluble and adsorbed As species undergo biotic transformations. As(V) can serve as the terminal electron acceptor in the biological oxidation of organic matter, and the limited number of microbes capable of this transformations are diverse in their phylogeny and physiology. Fe(III)-respiring bacteria can mobilize both As(V) and As(III) bound to ferric oxides by the reductive dissolution of iron-arsenate minerals. SO4(2-)-reducing bacteria can promote deposition of As(III) as sulfide minerals via their production of sulfide. A limited number of As(III)-oxidizing bacteria have been identified, some of which couple this reaction to growth. Lastly, prokaryotic and eukaryotic microbes can alter arsenic toxicity either by coupling cellular export to its reduction or by converting inorganic As to organo-arsenical compounds. The degree to which each of these metabolic transformations influences As mobilization or sequestration in different sedimentary matrices remains to be established.

Bromide's effect on DBP formation, speciation, and control: part 2, biotreatment

Both bromo‐ and chloro‐substituted disinfection by‐products decreased significantly when a combination of ozonation and biotreatment was used.The effect of bromide concentration, ozone dosage, and biotreatment on the control of disinfection by‐products (DBPs) was evaluated. Although total trihalomethane precursors were better controlled by ozonation and the precursors of six haloacetic acids were better controlled by biological treament, the combined processes were effective for the control of all halogenated DBP precursors. Ozone's conversion of bromide to bromate and the chemical or biological oxidation of organic matter changed the ratio of bromide to dissolved organic carbon. Increases in this ratio increased the formation of some brominated DBPs, but these DBP increases were offset by the precursor oxidation provided by the combination of the two processes.

Study on the performance of an up-flow aerated biofilter (UAB) in municipal wastewater treatments

A comprehensive wastewater treatment system that accomplishes oxidation of organic matter, nitrification, and denitrification was developed, and its characteristics and performance were investigated. A municipal wastewater was treated by an up-flow aerated biofilter (UAB), in which biofilms were developed on stainless meshes installed horizontally. This UAB exhibited a great potential ability of oxidation of organic matter, SS stabilization, and nitrification due to a unique aeration mechanism giving high DO concentrations with relatively low aeration rates. Another unique feature of the UAB was that attached biofilms on stainless meshes physically filtered out and/or adsorbed suspended solids in the wastewater in addition to the biological oxidation of organic matter. A stable nitrification could be achieved at HRT=10 hours corresponding to a hydraulic loading of 86 L m−2 d−1 and at a ratio of aeration rate to wastewater flow rate (A/W) of 2, which is considerably low as compared to aeration rates of typical activated sludge systems. This UAB system also could handle relatively high hydraulic loading rates. The UAB used in this study still have enough space to install more stainless meshes so as to reduce hydraulic loading rates resulting in the reduction of HRT and aeration rate, which leads to improvement of the system performance as well as reduction of the running cost.

The Mechanism of Reaeration in Natural Streams

The basic theory of turbulent flow has been applied successfully to explain many phenomena occurring in natural and artificial waterways. In this study, turbulent flow theory, both isotropic and non-isotropic, has been utilized to formulate the theory of reaeration in natural streams, which have been subjected to deaeration by the biological oxidation of organic matter.

The role of insects in sewage disposal beds

In recent years, the increasing emphasis on the importance of controlling pollution in our natural waterways has led to many studies of the factors involved in the biological stabilization of domestic and industrial waste materials. The present investigation has sought to clarify the part that insects play in two popular waste treatment processes—trickling filters and oxidation ponds. The larvae of psychodid flies are extremely common in trickling filters, and aid in effecting better stabilized effluents by helping to keep the filter zooglea in a healthy state; the zooglea is responsible for the biological oxidation of organic matter and becomes inefficient if allowed to develop unchecked by scouring organisms. Pilot plant studies are described. Many species of insects are found in oxidation ponds, the most abundant and important of which are the larvae of midges which burrow into bottom deposits of the ponds. They help to keep the bottom sludges in good condition, aid in removing suspended materials from the substrate undergoing purification, and thereby reduce the biochemical oxidation demand of the final effluent. Laboratory experimental results and field observations are presented.