Soil microorganisms as controllers of atmospheric trace gases (H2, CO, CH4, OCS, N2O, and NO).

In seeking greater sustainability in water resources management, wastewater is now being considered more as a resource than as a waste-a resource for water, for plant nutrients, and for energy. Energy, the primary focus of this article, can be obtained from wastewater's organic as well as from its thermal content. Also, using wastewater's nitrogen and P nutrients for plant fertilization, rather than wasting them, helps offset the high energy cost of producing synthetic fertilizers. Microbial fuel cells offer potential for direct biological conversion of wastewater's organic materials into electricity, although significant improvements are needed for this process to be competitive with anaerobic biological conversion of wastewater organics into biogas, a renewable fuel used in electricity generation. Newer membrane processes coupled with complete anaerobic treatment of wastewater offer the potential for wastewater treatment to become a net generator of energy, rather than the large energy consumer that it is today.

Domestic Wastewater Treatment as a Net Energy Producer–Can This be Achieved?

The global population is increasing and because of this, the world may experience great fresh water scarcity. Our water resources are limited and, hence, water treatment and recycling methods are the only alternatives for getting fresh water in the coming decades. Therefore, there is a great need for the development of a suitable, inexpensive and rapid wastewater treatment techniques and reuse or conservation methods in the present century. The different types of water treatment and recycling techniques have been discussed in terms of their basic principles, applications, costs, maintenance and suitability. Additionally, a systematic approach to water treatment and recycling involving their understanding, evaluation and selection parameters has been presented. A brief guideline for the selection of the appropriate technologies for specific applications has been evaluated. This review adds to the global discussions on water scarcity solutions.

/pdf/chemical-treatment-technologies-for-waste-water-recycling-an-2c42z01700.pdf

Chemical treatment technologies for waste-water recycling—an overview

Review paper on current technologies for decolourisation of textile wastewaters: Perspectives for anaerobic biotechnology

Polycyclic Hydrocarbons Vol. 1. Pp. xxvi + 487. 126S. (With a chapter on carcinogenesis by Regina Schoental.) Vol. 2. Pp. lvii + 487. 140s. By E. Clar. (London and New York: Academic Press; Berlin: Springer-Verlag, 1964.)

Polycyclic Aromatic Hydrocarbons

Toxic aromatic pollutants, concentrated in industrial wastes and contaminated sites, can potentially be eliminated by low cost bioremediation systems. Most commonly, the goal of these treatment systems is directed at providing optimum environmental conditions for the mineralization of the pollutants by naturally occurring microflora. Electrophilic aromatic pollutants with multiple chloro, nitro and azo groups have proven to be persistent to biodegradation by aerobic bacteria. These compounds are readily reduced by anaerobic consortia to lower chlorinated aromatics or aromatic amines but are not mineralized further. The reduction increases the susceptibility of the aromatic molecule for oxygenolytic attack. Sequencing anaerobic and aerobic biotreatment steps provide enhanced mineralization of many electrophilic aromatic pollutants. The combined activity of anaerobic and aerobic bacteria can also be obtained in a single treatment step if the bacteria are immobilized in particulate matrices (e.g. biofilm, soil aggregate, etc.). Due to the rapid uptake of oxygen by aerobes and facultative bacteria compared to the slow diffusion of oxygen, oxygen penetration into active biofilms seldom exceeds several hundred micrometers. The anaerobic microniches established inside the biofilms can be applied to the reduction of electron withdrawing functional groups in order to prepare recalcitrant aromatic compounds for further mineralization in the aerobic outer layer of the biofilm. Aside from mineralization, polyhydroxylated and chlorinated phenols as well as nitroaromatics and aromatic amines are susceptible to polymerization in aerobic environments. Consequently, an alternative approach for bioremediation systems can be directed towards incorporating these aromatic pollutants into detoxified humic-like substances. The activation of aromatic pollutants for polymerization can potentially be encouraged by an anaerobic pretreatment step prior to oxidation. Anaerobic bacteria can modify aromatic pollutants by demethylating methoxy groups and reducing nitro groups. The resulting phenols and aromatic amines are readily polymerized in a subsequent aerobic step.

Enhanced biodegradation of aromatic pollutants in cocultures of anaerobic and aerobic bacterial consortia

Low strength soluble wastewaters with chemical oxygen demand (COD) of less than 2000 mg/I are mostly from food processing industries. They commonly contain simple substrates such as short- chain fatty acids, alcohols and carbohydrates. The application of anaerobic technology has been mostly directed towards the treatment of medium and high strength wastewaters rather than those of low strength. Problems limiting the treatment of dilute wastewaters are related to the wastewater and the reactor design. This dissertation investigates the application of the conventional upflow anaerobic sludge blanket (UASB) and its modification, the expanded granular sludge bed (EGSB), for the treatment of low strength soluble wastewaters. The main topics studied concern the wastewater related problems. Ile effect of dissolved oxygen on the methanogenic activity of granular sludges and the effect of low substrate levels inside reactors on the treatment performance were evaluated. Moreover, some aspects of reactor design related problems such as the retention of biomass and wastewaterbiomass contact were considered.Methanogens located in granular sludge have a high tolerance to oxygen. The concentration of oxygen found to cause 50% inhibition to methanogenic activity was between 7% and 41 % oxygen in the head space of flasks, which corresponded to 0.05 mg/ l and 6 mg/ l of dissolved oxygen prevailing in the media, respectively. The most important mechanism for the tolerance was the consumption of oxygen by facultative bacteria while metabolizing substrates. The most highly tolerant sludges had the highest respiration rates. The hypothesis considered is that anaerobic microenvironments are created inside granules protecting the methanogens. The absence of facultative substrate for respiring oxygen decreases the tolerance of methanognens to O 2 . The coexistence of methanogenic and facultative bacteria competing for substrate in one single bioreactor was explored under highly aerobic conditions, in order to verify the possible application of anaerobic-aerobic cocultures for the removal of recalcitrant pollutants. Simultaneous methane production and oxygen uptake occurred in an oxygen tolerant sludge while at least 2 mg/ l of dissolved oxygen was present in the media. The healthy co-culture was evident even after longer periods of oxygen exposure, when methane oxidizing bacteria eventually also developed.The feasibility of UASB and EGSB reactors at 30°C was demonstrated. In UASB reactors, COD removal efficiencies exceeded 95% at organic loading rates (OLR) up to 6.8 g COD/ l .d and influent COD concentrations (COD in ) ranging from 422 to 943 mg/ l , during the treatment of ethanol substrate. The efficiencies exceeded 86% at OLR up to 3.9 mg COD/ l .d when whey was used as a substrate. Below 630 mg COD/ l , acidification of whey instead of methanogenesis was the rate limiting step. The retention of biomass is not a problem in the UASB, but the mixing intensity is not high enough to decrease the biofilm diffusion limitation of substrate transport into granular biofilms. The EGSB was shown to have superior potentials compared with the UASB. COD removal efficiencies were above 80% at OLRs up to 12 g COD/ l .d with COD in as low as 100 to 200 mg/ l . The effect of low substrate levels was not significant in the EGSB due to the intense turbulent mixing regime obtained by applying high hydraulic and organic loads. The very low apparent K S value of 9.8 mg COD/ l found for the biofilms in the reactor, was comparable to the intrinsic K S values determined for the most predominant acetoclastic methanogen found in anaerobic bioreactors, Methanothrix soehngenii. This indicates that all transport limitations of substrate movement into the biofilms were overcome. Optimized operation without sludge washout is achieved when liquid upflow velocities (V up ) below 5.5 m/h are applied. The problem of sludge retention is also restricted when sludge flotation occurs due to the buoyancy forces of gas attached to biofilms. The required equilibrium between mixing intensity and sludge retention limits the operation of the EGSB to OLRs up to 7 g COD/ l .d and V up values ranging from 2.5 and 5.5 m/h. Both reactor studies confirmed that in practice dissolved oxygen does not constitute any detrimental effect on the treatment performance. Improved mixing intensity in the UASB and improved sludge retention in the EGSB will enable higher OLRs and lower COD in which can be tolerated, compared with those of this study.

The anaerobic treatment of low strength soluble wastewaters.

Since the earlier anaerobic treatment systems, the design concepts were improved from classic reactors like septic tanks and anaerobic ponds, to modern high rate reactor configurations like anaerobic filters, UASB, EGSB, fixed film fluidized bed and expanded bed reactors, and others. In this paper, anaerobic reactors are evaluated considering the historical evolution and types of wastewaters. The emphasis is on the potential for application in domestic sewage treatment, particularly in regions with a hot climate. Proper design and operation can result in a high capacity and efficiency of organic matter removal using single anaerobic reactors. Performance comparison of anaerobic treatment systems is presented based mostly on a single but practical parameter, the hydraulic retention time. Combined anaerobic reactor systems as well as combined anaerobic and non-anaerobic systems are also presented.

Anaerobic Reactor Design Concepts for the Treatment of Domestic Wastewater

The application of the expanded granular sludge bed (EGSB) reactor for the anaerobic treatment of low-strength soluble wastewaters using ethanol as a model substrate was investigated in laboratory-scale reactors at 30oC. Chemical oxygen demand (COD) removal efficiency was above 80% at organic loading rates up to12 g COD/L . d with influent concentrations as low as 100 to 200 mg COD/L. These results demonstrate the suitability of the EGBS reactor for the anaerobic treatment of low-strength wastewaters. The high treatment performance can be attributed to the intense mixing regime obtained by high hydraulic and organic loads. Good mixing of the bulk liquid phase for the substrate-biomass contact and adequate expansion of the substrate-biomass contact and adequate expansion of the sludge bed for the degassing were obtained when the liquid upflow velocity (V(up)) was greater than 2.5 m/h. Under such conditions, an extremely low apparent K(s) value for acetoclastic methanogenesis of 9.8 mg COD/L was observed. The presence of dissolved oxygen in the wastewater had no detrimental effect on the treatment performance. Sludge piston flotation from pockets of biogas accumulating under the sludge bed occurred at V(up) lower than 2.5 m/h due to poor bed expansion. This problem is expected only in small diameter laboratory-scale reactors. A. more important restriction of the EGSB reactor was the sludge washout occurring at V(up) higher than 5.5 m/h and which was intensified at organic loads higher than 7 g COD/L. d due to buoyancy forces from the gas production. To achieve an equilibrium between the mixing intensity and the sludge hold-up, the operation should be limited to an organic loading rate of 7 g COD/L d. and to a liquid up-flow velocity between 2.5 and 5.5 m/h (c) 1994 John Wiley & Sons, Inc.

Feasibility of expanded granular sludge bed reactors for the anaerobic treatment of low-strength soluble wastewaters.

This research assessed the effect of oxygen exposure on the methanogenic activity of anaerobic granular sludges. The toxicity of oxygen to acetoclastic methanogens in five different anaerobic granular sludges was determined in serum flasks with effective gas-to-liquid volumes of 4.65 to 1. The amount of oxygen that caused 50% inhibition of the methanogenic activity after 3 days of exposure ranged from 7% to 41% oxygen in the head space. These results indicate that methanogens located in granular sludge have a high tolerance for oxygen. The most important factor contributing to the tolerance was the oxygen consumption by facultative bacteria metabolizing biodegradable substrates. Uptake of oxygen by these bacteria creates anaerobic microenvironments where the methanogenic bacteria are protected. The results also indicate that methanogens in sludge consortia still have some tolerance to oxygen, even in the absence of facultative substrate for oxygen respiration.

Mario T. Kato

Papers

Enhanced biodegradation of aromatic pollutants in cocultures of anaerobic and aerobic bacterial consortia

The anaerobic treatment of low strength soluble wastewaters.

Anaerobic Reactor Design Concepts for the Treatment of Domestic Wastewater

Feasibility of expanded granular sludge bed reactors for the anaerobic treatment of low-strength soluble wastewaters.

High tolerance of methanogens in granular sludge to oxygen