详情

原文传递 IMPACT OF WASTEWATER QUALITY ON THE LONG-TERM ACCEPTANCE RATE OF SOILS FOR ON-SITE WASTEWATER DISPOSAL SYSTEMS

题名：	IMPACT OF WASTEWATER QUALITY ON THE LONG-TERM ACCEPTANCE RATE OF SOILS FOR ON-SITE WASTEWATER DISPOSAL SYSTEMS
作者：	Aziz Amoozegar
关键词：	wastewater；quality；accept；systems；dispo；long；soil；impact；osal；conductivity
摘要：	People living in rural areas and around large municipalities with no access to public sewage systems must dispose of their wastewater on-site. The most common type of on-site sewage management in North Carolina is the conventional septic system, which is composed of a septic tank (interceptor tank) and a drainfield. It is not uncommon for septic systems to fail. Hydraulic failure within the drainfield area of a young septic system is generally attributed to faulty design, installation, and/or misuse of the system. The quality of wastewater, however, can have a major impact on soil hydraulic properties, particularly on wastewater infiltration from the trenches into the soil. A reduction in the infiltration rate from the trenches of a septic system into the soil may result in surface failure of the system. The overall objective of the research presented here was to assess the effects of various components of domestic wastewater on soil hydraulic properties. Saturated hydraulic conductivity (K„J and infiltration rate (IR) for tap water, well water, and four different simulated wastewaters from washing machine, kitchen sink, bathroom sink and shower (bathroom wastewater without toilet wastes), and a car wash in a clayey soil, a sandy soil, and one saprolite were measured in situ for five consecutive days using three replications. Saturated hydraulic conductivity was measured by the constant-head well permeameter method using 6-cm diameter cylindrical holes. A 15- to 20-cm constant depth of water was maintained at the bottom of the hole and K«, was calculated using the Glover solution. The IR was measured under a 5- to 7-cm of constant head using double-cylinder (ring) infiltrometers. After the measurement phase, soil samples were collected from three depth intervals at three locations in the area between the outer and inner cylinders of each infiltrometer and from three depth intervals at three locations around each 6-cm diameter auger hole for laboratory analysis. In addition, intact core samples (6.5 cm diameter and 10 cm long) were collected from the clayey soil and saprolite and analyzed in the laboratory for K^, and water retention using the five solutions. For selected experiments, a CaCl2 solution was applied to the soil and saprolite following the initial measurement of IR or Ksat, to determine if the rate of water flow into the soil or saprolite could be improved. In general, K„, and IR of the two soils and saprolite for water did not change substantially with time. For the simulated wastewaters, however, both Ksat and IR decreased for saprolite and sandy soil. For the clayey soil, mixed results were obtained for most cases. Overall, simulated wastewater from washing machines (laundry wastewater) had the most negative impact on soil hydraulic properties. Based on measurement results after addition of CaCl2 to the soil and saprolite, it appears that the adverse effect of wastewater application on soil hydraulic properties may be reversible using calcium amendments. Based on the Na content and sodium adsorption ratio (SAR) of the simulated wastewaters, and considering that the adverse impact of wastewaters on infiltration rate and hydraulic conductivity were reversed with the addition of Ca to the soil or saprolite, it appears that in the absence of a biological clogging mat, Na (or a compound containing Na, such as a surfactant in laundry detergent) is the most likely cause for hydraulic failure of a septic system. Considering the reduction in the rate of flow into and through different soils for various components of wastewater, wastewater quality should be considered when determining the loading rates (long-term acceptance rates) for designing septic systems, particularly for laundry, car wash, and other businesses in rural areas.
报告类型：	科技报告