Technical Report No. 63
Michael J. Chun, Reginald H. F. Young, George K. Anderson
A three-year study was conducted to determine the quality of domestic wastewater treatment plant effluents and urban surface runoff, including street litter, on Oahu and to examine the reclamation potential of these water resources. The study was conducted in three phases: 1) the examination of effluents of eleven wastewater treatment plants representative of conventional treatment technology, 2) the characterization of street Litter and of runoff from a watershed representative of runoff from varied land-use patterns, and 3) the fabrication of a reverse osmosis pilot module and preliminary evaluation of its potential to reclaim secondary sewage effluent. Domestic sewage flows were found to be characteristically similar to those found elsewhere in the United States. Treatment plant efficiency in reduction of organic matter and suspended solids, for all process trains studied, was comparable to reported literature. Effluent nutrient (N and P) and dissolved oxygen levels do not meet standards of receiving water quality suggesting a need for mixing zone variances, process change or addition or both. Reclamation of the effluents for recharge or direct reuse schemes should be within the capabilities of present technology. Manoa Stream was selected for the watershed study. Results show generally very low levels of all parameters as compared to wastewater effluents but an extreme range of variability dependent on flow conditions. Constituent levels or “degree of contamination” were found to vary directly with urban population density, urban development and land-use activity. The most significant factor determined was that in both dry and wet weather conditions, the State Water Quality Standards. However, low fecal coliform to fecal streptococcus ratios indicate the probable source of bacterial contamination as non-human, warm-blooded animals and thus the stream waters may still be considered suitable for recreational use. Street sweepings were obtained from locations of urban activity in downtown Honolulu and Waikiki. Compared to data available from a Chicago study, these street litter had a higher BOD, nitrate, phosphate, and water soluble material content. Results showed a considerable potential for pollution of surface runoff by the street litter but this impact requires further evaluation since the litter was obtained by sweeping of only the gutter areas, not the entire paved street surface, and may not be totally representative of the suspended and dissolved materials load that may be transported with runoff into stormwater collection systems. In the final phase of study a spiral-wound test module reverse osmosis unit was fabricated for evaluation in reclamation of wastewater effluents. The effluent was selected over runoff or streamflow because of its relative constant flow volume. Initial test results with intermittent operation of over 320 hours yielded a product comparable to a low mineral content water supply from chlorinated activated sludge effluent. Reduction in flux rate occurred, however, necessitating the use of an enzyme detergent flushing to restore the unit’s production capacity, but the flux rate could not be restored to its original operating level. Continued testing of the unit is planned with effluents of different degrees of wastewater treatment to better determine its treatment capabilities and economics of operation.