As a result of population growth, urbanization, and climate change, public water supplies are becoming stressed, and the chances of tapping new water supplies for metropolitan areas are getting more difficult, if not impossible. As a consequence, existing water supplies must go further.One way to achieve this objective is by increased water reuse, particularly in supplementing municipal water supplies. Although water reuse offers many opportunities it also involves a number of problems. A significant cost for nonpotable water reuse in urban areas is associated with the need to provide separate piping and storage systems for reclaimed water. In most situations, the cost of a dual distribution system has been prohibitive and thus, has limited implementation for water reuse programs. The solution to the problem of distribution is to implement direct potable reuse (DPR) of purified water in the existing water distribution system. The purpose of this paper is to consider (a) a future in which DPR will be the norm and (b) the steps that will need to be taken to make this a reality. Following an overview, the rationale for DPR, some examples of DPR projects, technological and implementation issues, and future expectations are examined. DIRECT POTABLE REUSE: AN OVERVIEWDirect potable reuse (DPR) refers to the introduction of purified water, derived from municipal wastewater after extensive treatment and monitoring to assure that strict water quality requirements are met at all times, directly into a municipal water supply system. The resultant purified water could be blended with source water for further water treatment or even direct pipe-to-pipe blending of purified water and potable water. DPR offers the opportunity to significantly reduce the distance that purified water would need to be pumped and significantly reduce the head against which it must be pumped, thereby reducing costs. The other significant advantage of DPR is that it has the potential to allow for full reuse of available purified water in metropolitan areas, using the existing water distribution infrastructure.A general flow diagram for alternative potable reuse strategies is shown on Figure 1. As shown, two DPR options are available. In the first option (heavy solid black line), purified water is first placed in an engineered storage buffer (ESB).From the ESB, purified water can either be blended with the water supply source prior to water treatment or can be blended directly with treated potable water. In the second option (heavy dashed back line) purified water, without the use of an ESB, can be blended in either of the two locations discussed for option 1. As will be discussed later, implementation of option 2 would entail more extensive reliability measures and effective on-line continuous monitoring. The concept and role of the ESB is considered in the following discussion. Engineered storage buffers for quality assuranceAn important element of a DPR system is the ability to provide water of a specified quality reliably all the time. B...

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.

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.

a b s t r a c tAnoxic subsurface flow (SSF) constructed wetlands were evaluated for denitrification using nitrified wastewater. The treatment wetlands utilized a readily available organic woodchip-media packing to create the anoxic conditions. After 2 years in operation, nitrate removal was found to be best described by first-order kinetics. Removal rate constants at 20• C (k 20 ) were determined to be 1.41-1.30 d −1 , with temperature coefficients (Â) of 1.10 and 1.17, for planted and unplanted experimental woodchip-media SSF wetlands, respectively. First-order removal rate constants decreased as length of operation increased; however, a longer-term study is needed to establish the steady-state values. The hydraulic conductivity in the planted woodchip-media SSF wetlands, 0.13-0.15 m/s, was similar to that measured in an unplanted gravel-media SSF control system.

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