Beal C D, Gardner E A, Kirchhof G, Menzies N W
School of Land and Food Sciences, University of Queensland, Australia.
Water Res. 2006 Jul;40(12):2327-38. doi: 10.1016/j.watres.2006.04.018. Epub 2006 Jun 9.
Soil absorption systems (SAS) are used commonly to treat and disperse septic tank effluent (STE). SAS can hydraulically fail as a result of the low permeable biomat zone that develops on the infiltrative surface. The objectives of this experiment were to compare the hydraulic properties of biomats grown in soils of different textures, to investigate the long-term acceptance rates (LTAR) from prolonged application of STE, and to assess if soils were of major importance in determining LTAR. The STE was applied to repacked sand, Oxisol and Vertisol soil columns over a period of 16 months, at equivalent hydraulic loading rates of 50, 35 and 8L/m(2)/d, respectively. Infiltration rates, soil matric potentials, and biomat hydraulic properties were measured either directly from the soil columns or calculated using established soil physics theory. Biomats 1 to 2 cm thick developed in all soils columns with hydraulic resistances of 27 to 39 d. These biomats reduced a 4 order of magnitude variation in saturated hydraulic conductivity (K(s)) between the soils to a one order of magnitude variation in LTAR. A relationship between biomat resistance and organic loading rate was observed in all soils. Saturated hydraulic conductivity influenced the rate and extent of biomat development. However, once the biomat was established, the LTAR was governed by the resistance of the biomat and the sub-biomat soil unsaturated flow regime induced by the biomat. Results show that whilst initial soil K(s) is likely to be important in the establishment of the biomat zone in a trench, LTAR is determined by the biomat resistance and the unsaturated soil hydraulic conductivity, not the K(s) of a soil. The results call into question the commonly used approach of basing the LTAR, and ultimately trench length in SAS, on the initial K(s) of soils.
土壤吸收系统（SAS）通常用于处理和分散化粪池出水（STE）。由于在渗透表面形成的低渗透性生物膜区域，SAS可能会出现水力失效。本实验的目的是比较在不同质地土壤中生长的生物膜的水力特性，研究长期施用STE后的长期接纳率（LTAR），并评估土壤在确定LTAR方面是否至关重要。在16个月的时间里，分别以50、35和8L/m²/d的等效水力负荷率，将STE施加到重新装填的砂柱、氧化土柱和变性土柱上。直接从土柱中测量或使用既定的土壤物理理论计算渗透速率、土壤基质势和生物膜水力特性。在所有土柱中都形成了1至2厘米厚的生物膜，其水力阻力为27至39天。这些生物膜将土壤之间饱和导水率（K(s)）的4个数量级变化降低到LTAR的1个数量级变化。在所有土壤中都观察到生物膜阻力与有机负荷率之间的关系。饱和导水率影响生物膜的发育速率和程度。然而，一旦生物膜形成，LTAR就由生物膜的阻力和生物膜引起的生物膜下土壤非饱和流态控制。结果表明，虽然初始土壤K(s)在沟渠中生物膜区域的形成中可能很重要，但LTAR是由生物膜阻力和非饱和土壤导水率决定的，而不是土壤的K(s)。这些结果对基于土壤初始K(s)来确定LTAR以及最终确定SAS中沟渠长度的常用方法提出了质疑。
