تعیین الگوی رطوبتی در خاکهای آب‌گریزشده توسط لجن فاضلاب شهری در جریان دو بعدی

نویسندگان

چکیده

آب‌گریزی خاک بر پیشروی جبهه رطوبتی و انتقال املاح در خاک مؤثر است. این پژوهش برای بررسی چگونگی پیشروی جبهه رطوبتی در خاک‌های آب‌گریز انجام شد. خاک مورد بررسی از منطقه‌ای در مجاورت تصفیه‌خانه فاضلاب فولادشهر که تحت تأثیر درجات مختلفی (25، 50،65 و 80 درصد) از لجن تصفیه‌خانه فاضلاب شهری قرار گرفت، برداشت شد. در حدود یک سال پس از آب‌گریز کردن خاک‌ها در اثر اضافه کردن میزان لجن‌های یادشده جبهه رطوبتی ناشی از آبیاری جویچه‌ای در آن‌ها تعیین شد. بدین منظور از یک محفظه شیشه‌ای با ابعاد 70×50×6 سانتی‌متر استفاده و عمقی به ارتفاع 5 سانتی‌متر آب با استفاده از دستگاه ماریوت روی سطح جویچه قرار داده شد. سپس پیشروی جبهه رطوبتی در زمان‌های مختلف اندازه‌گیری شد. نتایج نشان داد که در اثر افزایش آب‌گریزی در خاک، الگوی رطوبتی نیز نامنظم‌تر شد. با افزایش تخلخل خاک تأثیر آب‌گریزی ناشی از لجن بر نفوذپذیری کاهش یافت. اگرچه شدت نفوذ آب به خاک آب‌گریز با گذشت زمان کاهش یافت اما تفاوت شدت نفوذ اولیه و نهایی بسیار کم بود. در تیمار آبدوست (بدون افزودن لجن- شاهد) همواره هدایت هیدرولیکی اشباع کمتر یا مساوی شدت نفوذ آب به خاک بود اما در تیمارهای آب‌گریز به‌دلیل حبس هوا در حین نفوذ آب به داخل خاک، هدایت هیدرولیکی اشباع بزرگ‌تر از شدت نفوذ آب به خاک به ‌دست آمد.

کلیدواژه‌ها


عنوان مقاله [English]

Wetting pattern in a hydrophobic soil produced by sewage sludge under2D flow

نویسندگان [English]

  • Negar Nourmahnad
  • Sayyed Hasan Tabatabaei
  • Abdolrahim Hoshmand
  • Mohamad Reza Nouri Emamzadei
  • Shoja Ghorbani Dashtaki
چکیده [English]

Water repellency of soils is a property with signi?cant consequences for agricultural water management, water in?ltration, vertical soil-water transport, contaminant transport, and for soil erosion. It is caused by the presence of hydrophobic organic materials on soil grains and aggregate surfaces. Dry soil usually absorbs moisture but hydrophobic soil resists or reduces water infiltration into soil. Water repellency potentially affects wetting front and solutes transport in soil. This research was conducted in hydrophobic soils in order to investigate wetting pattern. The soil was collected from the region in the vicinity of sewage pilot of Fouladshar, Isfahan, Iran. Different amounts of urban sewage sludge including 25, 50, 65 and 80 weight percent were added to hydrophilic soil and S25%, S50%, S65% and S80% were obtained. After almost one year, soil water repellency was determined by using water drop penetration time method. In this procedure Three drops of distilled water from a standard medicine dropper are placed on the smoothed surface of a soil sample, and the time that elapses before the drops are absorbed is determined. In general, soil is considered to be water repellent if the WDPT exceeds 5 s. In this way the following classes were distinguished: wettable or non-water repellent (< 5 s); slightly (5-60 s); strongly (60-600 s).
After that saturation hydraulic conductivity was determined by means of constant head method. The soil wetting pattern of furrow irrigation was determined. For this purpose, a chamber by dimensions 6×50×70 cm was used. Prior to placing the soil into the chamber, the sides were coated with paraffin wax. After sand placement, the purpose of the wax was to prevent preferential flow channels from developing along the sides of the chamber.
A five cm height of water was put in furrow by means of Marriott, and then advancing wetting fronts were determined in different time. The shape of wetting front was simulated using Surfer software version 8 (Golden Software Institute, 2002), in different time. Results showed that wetting pattern became irregular by increasing water repellency. Effect of sludge hydrophobicity on permeability was decreased by increasing porosity. In S25% initial infiltration rate was 45.6 cm/hr and it decreased to 30.6 cm/hr after 4 minutes. Final infiltration rate was 13.5 cm/hr. So it increased rather than S0.In S50% the initial infiltration rate was 16.8 cm/hr and it decreased to 13.86 cm/hr finally. Although S50% had more coarse texture and lower initial water content than S0 and S25%, it had lower initial infiltration rate because of stronger hydrophobicity. Indeed water movement and water retention in water repellent soil is different than wettable soil. Hydrophobic soil infiltration rates did not increase with time, although the difference between the initial and final infiltration rates was very low. In general, water movement is initially severely limited in dry water repellent soils. Large differences in wettability exist between wettable and water repellent soils. Wetting is fast in wettable soil, whereas in a water repellent and fine texture soil wetting may be a very slow process.
In?ltration rates into water repellent soils can be considerably lower than those into wettable soils. In hydrophilic treatment saturated hydraulic conductivity was less than or equal to the water intake to the soil but saturated hydraulic conductivity were greater than the water intake due to air confinement in hydrophobic treatments during water infiltration into the soil. Due to overcome the effect of hydrophobicity on the coarseness of soil pores, water movement was slowly in S50% than S65% and S80%. Wetted area was measured using Auto Cad 2013 software after drawing by Surfer software. The lowest wetted area and the highest wetted width was observed in S0. Width of wetted soil was determined after constant time in all treatments. For example Width of wetted soil after 1 hour from beginning of irrigation in S0, S25%, S50%, S65% and S80% were 28, 24, 18, 16
In?ltration rates into water repellent soils can be considerably lower than those into wettable soils. In hydrophilic treatment saturated hydraulic conductivity was less than or equal to the water intake to the soil but saturated hydraulic conductivity were greater than the water intake due to air confinement in hydrophobic treatments during water infiltration into the soil. Due to overcome the effect of hydrophobicity on the coarseness of soil pores, water movement was slowly in S50% than S65% and S80%. Wetted area was measured using Auto Cad 2013 software after drawing by Surfer software. The lowest wetted area and the highest wetted width was observed in S0. Width of wetted soil was determined after constant time in all treatments. For example Width of wetted soil after 1 hour from beginning of irrigation in S0, S25%, S50%, S65% and S80% were 28, 24, 18, 16.

کلیدواژه‌ها [English]

  • Soil water repellency-Wetting pattern-Sewage sludge-Infiltration rate-