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Demonstration of a Graywater Management Project at a Community Level on the Island of Puerto Rico
Citation:
Huertas, E., E. Colon, AND T. OConnor. Demonstration of a Graywater Management Project at a Community Level on the Island of Puerto Rico. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/268, 2015.
Impact/Purpose:
Past construction practices have created a legacy of communities in rural areas of Puerto Rico that were constructed without properly planned residential sewage disposal infrastructure. Many of these communities were built with on-site wastewater disposal systems even though the conditions were often not conducive to the proper operation of these systems due to a variety of conditions. In an effort to reduce overflows from these onsite systems, homeowners have generally adopted the practice of discharging graywater to the property surrounding the house or when available, to a storm drain, street gutter or a nearby water body or course. This discharge practice has elevated pathogenic indicator microorganisms in the local streams and lakes, and has increased phosphorous and other pollutant concentrations in downstream reservoirs. The Puerto Rico Watershed Stewardship Program (WSP), a collaborative effort comprised of federal and local agencies, has sought various ways to improve receiving water quality and protect reservoirs. This EPA Regional Applied Research Effort (RARE) project funded the design, construction and monitoring of a community graywater garden system in the rural community of María Jiménez in the municipality of Gurabo, a small town 35 km south of San Juan. The graywater garden system received graywater from four residences comprised of 13 persons in all. The period of monitoring was from May 2013 to September 2014 during which samples were collected for standard water quality parameters (e.g. solids, organics, nutrients, metals and indictor microorganisms) for eight monitoring events. The original design assumed there would not be graywater from the kitchen sink. Initially, a simple 400 L pretreatment system was designed to capture oil and grease from kitchen water but this was later replaced with a larger 1000 L pretreatment system which captured oil and grease better and provided more storage which reduced surges. Other operational changes were made during the demonstration project including construction of a French drain, addition of material to surface and plant harvesting in an effort to eliminate observed surface ponding during the rainy season. Influent concentrations were similar to literature values of septic system discharges to drainage fields. While differences were observed between influent and effluent concentrations within the graywater system for individual events, the long term analysis showed no statistical difference, except for an increase in iron. Effluent concentrations for several parameters changed during the course of the project and this was due to operational and maintenance changes. There was an increase in sulfide concentration which correlated with a drop in pH; this change potentially indicated that the 1000 L tank led to more stable anaerobic conditions. A quick look through the figures in Appendix A indicated that many of the lowest concentrations for both the influent and effluent came during the last two sampling events. This also points to better operation and maintenance by the larger pretreatment system; oil and grease capture was crucial to reducing all pollutant concentrations in the graywater garden. Phosphorous effluent concentration increased after plant harvesting, indicating that the plants had been effective in reducing nutrient concentrations. Recommendations for improved design were made, and many of these design recommendations were derived from recommended practices for septic system drainage fields. Overall, the graywater garden demonstration project reduced flows of graywater that would have alternatively discharged directly to storm drains and receiving water. As such, the use of graywater gardens if practiced elsewhere on Puerto Rico and in sufficient numbers may reduce discharges to receiving streams and downstream reservoirs.
Description:
Housing development practices in Puerto Rico, especially in rural areas, have often not considered the proper treatment and disposal of wastewater or the collection and treatment of stormwater. These practices have created a legacy of communities without proper sewage disposal infrastructure. To reduce hydraulic loadings to on-site wastewater disposal systems, many residents have engaged in the practice of releasing graywater to the stormwater drainage system or nearest receiving stream. This untreated graywater can eventually end up in the watersheds and drinking water reservoirs of Puerto Rico (Tetra Tech Inc, 2011). For example, in Puerto Rico’s Río Grande de Loíza and La Plata watersheds, where 57% of the population are not connected to a centralized sewer service (PREQB, 2007), eutrophication has been identified as a major water quality problem that impacts the reservoir (Quiñones, 1980). The reservoirs in these two priority watersheds represent the source water for approximately 40% of the population of Puerto Rico. Graywater gardens are potentially a low-cost-and-maintenance alternative to conventional sewer projects to manage contaminant discharges in these watersheds.A graywater garden was constructed and monitored in the María Jiménez community of the municipality of Gurabo in Puerto Rico. The garden was designed to infiltrate and evapotranspirate incoming graywater. Four households were connected to a graywater garden. Initially graywater was collected in two 200-L pretreatment tanks to control oil and grease. This pretreatment was later increased to 1,000 L. Results from the quarterly analysis during an 18-month period showed no statistically consistent removal of monitored parameters across the graywater garden system. Observation indicated some parameters had events indicative of removal as effluent concentrations were lower than influent concentrations removals; however, there were also events where influent concentrations were lower than effluent concentrations, potentially indicating a lagging in response (e.g., total Kjeldahl nitrogen and chemical oxygen demand). Some parameters had no lagging response (e.g. magnesium, potassium and total coliform). A statistical increase in effluent iron was most likely an indicator of excessive organic loading. Treatment within the graywater garden was greatly influenced by system maintenance frequency as well as seasonal periods of high precipitation and humidity which muted the effect of evapotranspiration and evaporation. Results of quarterly water quality measurements indicated that the graywater garden behaved like an anaerobic drainage field for a septic system. Despite lack of pollutant reduction within the graywater garden system, graywater discharges from these four households for the most part were eliminated. The final community graywater garden system which included the larger pre-treatment system to handle oil and grease loadings from kitchen sinks demonstrated that graywater garden system can be effective at controlling household graywater. Therefore wider graywater garden implementation may reduce untreated graywater discharges (as is currently the case) in many of these communities. Recommendations for improving the graywater garden system were made and future design modifications could improve the pollutant removal performance.