George Tchobanoglous

Evaluation of the short-term toxicity of nitrogenous compounds to channel catfish, Ictalurus punctatus

Abstract The acute toxicity of un-ionized ammonia, nitrite, and nitrate to 50–76-mm fingerling channel catfish ( Ictalurus punctatus ) was investigated using a static bioassay system at 22, 26 and 30°C. The 96-h LC50 values at 30°C for un-ionized ammonia, nitrite, and nitrate were 3.8, 44, and 6 200 mg/l.

Size distributions of particulate contaminants in wastewater and their impact on treatability

Abstract Particle size information, derived from membrane separation of wastewater samples and quantification of solids and organic content, is used to examine particulate contaminants in wastewater in terms of size distributions and biological treatability. Field and bench-scale studies of aerobic and anaerobic biological processes provide a basis for determining the conditions under which influent particle size distributions influence process kinetics. The value of using pretreatment processes to modify particle size distributions is investigated for high-rate and conventional biological treatment processes. The utility of particle size information for design and process evaluation, as an adjunct to conventional wastewater characterization parameters, is discussed, particularly for municipal wastewater treatment and reuse.

Ultrafiltration of wastewater: effects of particles, mode of operation, and backwash effectiveness.

The effects that wastewater quality and mode of operation have on the performance of an asymmetric, hollow fiber, polysulfone, ultrafiltration (UF) membrane with a molecular weight cutoff of 100,000 Daltons were investigated. Performance was assessed through monitoring membrane flux, transmembrane pressure, effluent biochemical oxygen demand, and operational cost of the experimental system while treating filtered secondary, secondary, and filtered primary effluents. Fluxes achieved for filtered secondary (129-173 l/m2 h), secondary (101-158 l/m2 h), and filtered primary (20-41 l/m2 h) effluents were compared to those obtained at three other locations where similar UF systems were operated. A conceptual model of the impact of an insufficient backwash and of operating the UF system at constant flux on membrane performance is presented to explain the differences in fluxes. Employing pre-membrane granular filtration to remove a portion of the problematic particles in secondary effluent prior to UF led to optimal operational conditions. The costs associated with the operation of pre-membrane granular filtration were offset by the increase in production achieved. Although the use of recirculation could increase maintainable flux when treating a concentrated feed (e.g., filtered primary effluent), the associated costs were high. Improved UF performance was found to result from allowing flux to decline naturally, rather than using a constant flux mode of operation. The effluents produced when filtered secondary and secondary effluents were the feeds would be equivalent to an oxidized, coagulated, clarified, and filtered wastewater as per Title 22 California Wastewater Reclamation Criteria.

Clogging in intermittently dosed sand filters used for wastewater treatment

Clogging in intermittent sand filter (ISF) systems was analyzed using an unsaturated flow model coupled with a reactive transport model. Based on the results of a model sensitivity analysis, several variables were determined to be important in the clogging phenomena observed in ISFs, including hydraulic loading rate, influent chemical oxygen demand (COD) concentration, filter dosing frequency, and time of operation. Several modes of operation were identified that minimize the growth of bacteria at the filter surface. Following the sensitivity analysis, several case studies where ISF clogging was documented were simulated using the model. The results from the case study model simulations were found to be correlated with the total suspended solids loading rate (TSSLR) at the point of clogging. A model was developed that relates biomass development at the surface of ISFs with the TSSLR that can be sustained without clogging. The engineering significance of the model is presented in terms of operational and design considerations.

The effects of nitrite on the short-term growth and survival of channel catfish, Ictalurus punctatus

Abstract The effect of nitrite on the growth and survival of juvenile channel catfish ( Ictalurus punctatus ) was evaluated in a 31 day growth trial. The growth of the juvenile fish was reduced at NO 2 − N levels of 1.60 mg/l and above. Mortality was increased significantly at 3.71 mg/l NO 2 − N and above. The reduction in growth at the highest nitrite concentration without mortality was only 20%. The growth response of the fish at nitrite concentration levels with significant mortality was extremely variable.

Ultrafiltration as an advanced tertiary treatment process for municipal wastewater

Abstract Treatment of secondary and tertiary municipal wastewater by membrane filtration has been investigated at the University of California, Davis, California, USA, as described in the following paper. Secondary and tertiary wastewater used during this investigation were produced from activated sludge and media filtration processes, respectively. Ultrafiltration, hollow-fiber, polysulfone membranes were used in this investigation for the treatment of secondary and tertiary municipal wastewater. Membrane operating parameters investigated were cross-flow velocity, with circulation and single pass flow, trans-membrane pressure and backflushing methods. Total solids and particle size distribution of secondary and tertiary wastewater were analyzed and correlated with observed membrane performance. Reduction of total solids, biological oxygen demand (BOD), and chemical oxygen demand (COD) of secondary wastewater was also determined after treatment with membrane and media filtration processes.

Sustainable use of water in the Aegean Islands.

Water demands in the Aegean Islands have increased steadily over the last decade as a result of a building boom for new homes, hotels, and resorts. The increase in water demand has resulted in the disruption of past sustainable water management practices. At present, most freshwater needs are met through the use of the limited groundwater, desalinated seawater, and freshwater importation. Wastewater reclamation, not used extensively, can serve as an alternative source of water, for a variety of applications now served with desalinated and imported water. Three alternative processes: desalination, importation, and water reclamation are compared with respect to cost, energy requirements and long-term sustainability. Based on the comparisons made, water reclamation and reuse should be components of any long-term water resources management strategy.

Treatment of Wastewater With Slow Rate Systems: A Review of Treatment Processes and Plant Functions

Land treatment systems constitute a viable alternative solution for wastewater management in cases where the construction of conventional (mechanical) wastewater treatment plants (WWTPs) are not affordable or other disposal options are not available. They have proven to be an ideal technology for small rural communities, clusters of homes, and small industrial units due to low energy demands and low operation and maintenance costs. In addition, slow rate systems (SRS) may be designed using the “zero discharge” concept. The purpose of this article is to review the current trends and developments in the field of SRS, focusing on those systems in which effluent application is based on plant water requirements. Vegetation has an important role in treatment efficiency through its effects on hydraulic loading rate, nutrient removal, and biomass production. In addition, vegetation may affect the fate of trace elements and the degradation/detoxification of recalcitrant organics. Detailed knowledge of the basic processes involved in wastewater treatment and the factors governing the performance of SRS is fundamental for enhancing treatment efficiency and eliminating potential environmental and health risks. Finally, monitoring performance of SRS and adopting the appropriate management strategies are of paramount importance to maintain treatment efficiency over the a long term.

BTEX removal in pilot-scale horizontal subsurface flow constructed wetlands

Abstract Benzene, toluene, ethylbenzene, and xylenes (BTEX) are commonly encountered pollutants. The focus of the present work is on the removal of BTEX using pilot-scale constructed wetlands (CWs). Experiment carried out in three similar pilot-scale horizontal sub-surface flow constructed wetlands with an area of 35 m2 (each), two of which were planted with different macrophytes (Phragmites australis and Typha latifolia), while an unplanted one was used as control. A number of hydraulic tests were carried out using lithium bromide as tracer, to assess the hydraulic residence time. Residence time distributions for the two CWs indicated that the Typha field was characterized by a void volume fraction (porosity) of 0.16 and exhibited more ideal plug flow behavior (Pe = 29.7) compared with the Phragmites field (Pe = 26.7), which had similar porosity. The measured hydraulic residence times in the planted fields were 35.8, 36.7, and 34.1 h for Typha, Phragmites, and unplanted respectively, at wastewater flow r...

Methane, carbon dioxide, and nitrous oxide emissions from septic tank systems.

Emissions of CH4, CO2, and N2O from conventional septic tank systems are known to occur, but there is a dearth of information as to the extent. Mass emission rates of CH4, CO2, and N2O, as measured with a modified flux chamber approach in eight septic tank systems, were determined to be 11, 33.3, and 0.005 g capita(-1) day(-1), respectively, in this research. Existing greenhouse gas (GHG) emission models based on BOD (biochemical oxygen demand) loading have estimated methane emissions to be as high as 27.1 g CH4 capita(-1) day(-1), more than twice the value measured in our study, and concluded that septic tanks are potentially significant sources of GHGs due to the large number of systems currently in use. Based on the measured CH4 emission value, a revised CH4 conversion factor of 0.22 (compared to 0.5) for use in the emissions models is suggested. Emission rates of CH4, CO2, and N2O were also determined from measurements of gas concentrations and flow rates in the septic vent system and were found to be 10.7, 335, and 0.2 g capita(-1)day(-1), respectively. The excellent agreement in the CH4 emission rates between the flux chamber and the vent values indicates the dominant CH4 source is the septic tank.