Approximate analytical model for transient transport and oxygen-limited biodegradation of vapor-phase petroleum hydrocarbon compound in soil.

Volatile organic compounds (VOCs) contamination may occur in subsurface soil due to various reasons and pose great threat to people. Petroleum hydrocarbon compound (PHC) is a typical kind of VOC, which can readily biodegrade in an aerobic environment. The biodegradation of vapor-phase PHC in the vadose zone consumes oxygen in the soil, which leads to the change in aerobic and anaerobic zones but has not been studied by the existing analytical models. In this study, a one-dimensional analytical model is developed to simulate the transient diffusion and oxygen-limited biodegradation of PHC vapor in homogeneous soil. Laplace transformation and Laplace inversion of the Talbot method are adopted to derive the solution. At any given time, the thickness of aerobic zone is determined by the dichotomy method. The analytical model is verified against numerical simulation and experimental results first and parametric study is then conducted. The transient migration of PHC vapor can be divided into three stages including the pure aerobic zone stage (Stage I), aerobic-anaerobic zones co-existence stage (Stage II), and steady-state stage (Stage III). The proposed analytical model should be adopted to accommodate scenarios where the transient effect is significant (Stage II), including high source concentration, deep contaminant source, high biodegradation capacity, and high water saturation. The applicability of this model to determine the breakthrough time for better vapor intrusion assessment is also evaluated. Lower first-order biodegradation rate, higher source concentration, and shallower source depth all lead to smaller breakthrough time.

Transient migration behavior of VOC vapor in layered unsaturated soils subjected to multiple time-dependent point pollution sources: Analytical study.

Predicting the migration behavior of volatile organic compounds (VOCs) vapor is essential for the remediation of subsurface contamination such as soil vapor extraction. Previous analytical prediction models of VOCs migration are mostly limited to constant-concentration nonpoint sources in homogeneous soil. Thus, this study presents a novel analytical model for two-dimensional transport of VOCs vapor subjected to multiple time-dependent point sources involving transient diffusion, sorption and degradation in layered unsaturated soils. Two representative time-dependent sources, i.e., an instantaneous source and a finite pulse source, are used to describe the short-term and long-term leakage. Results reveal that soil heterogeneity can cause pollution accumulation, especially in low-diffusivity capillary fringe. The assumption of an equivalent plane source from multiple point sources would significantly overestimate the vapor concentration and the contaminated range. The previous single point source model is no longer inapplicable when the relative distance and/or the release interval between sources is small, giving a strong interaction between multiple sources. Moreover, a faster vapor degradation rate or a higher groundwater level will reduce the area of vapor plume linearly. Hence, close attention should be paid to the time-variation characteristics of multiple sources, the vapor degradation and the groundwater level fluctuation in practice to facilitate soil remediation. The proposed model is a promising tool for addressing the above issue.

Redo pull-through in total colonic aganglionosis due to residual aganglionosis: a single center's experience.

BACKGROUND: Reoperation for total colonic aganglionosis (TCA) may be required for residual aganglionosis after an initial radical operation. We aimed to investigate the symptoms, management, and outcomes of patients who required a redo pull-through (Redo PT). METHODS: Nine TCA patients underwent Redo PT at our center between 2007 and 2017. Their medical records were reviewed. Parental telephone interviews that included disease-specific clinical outcomes were conducted, and post-operative complications and long-term outcomes (including height-for-age/weight-for-age and bowel-function score) were compared to those of single-pull-through (Single PT) patients (n = 21). RESULTS: All the nine Redo PT patients suffered obstruction within 1 month after the initial operation that could not be alleviated by conservative treatment. All abdominal X-ray/contrast barium enemas showed proximal bowel dilatation, indicating residual aganglionosis. The median ages at the initial operation and Redo PT were 200 and 509 days, respectively. Reoperation consisted of an intraoperative frozen biopsy and a modified laparotomic Soave procedure in all patients. Post-operative complications included perianal excoriation (n = 3), intestinal obstruction (n = 2), enterocolitis (n = 2), and rectovestibular fistula (n = 1). Seven Redo PT patients were followed up for a mean time of 7.1 ± 2.3 years; six (85.7%) had good growth and four (57.1%) had good bowel-function recovery. Post-operative complications and long-term outcomes were almost equal between the Redo PT and Single PT groups (all P > 0.05). CONCLUSION: TCA patients with recurrent obstructive symptoms and dilated proximal bowel may have residual aganglionosis after an initial operation. Redo PT is effective and provides good long-term outcomes comparable to those of patients who benefited from Single PT.

An analytical model for one-dimensional diffusion of degradable contaminant through a composite geomembrane cut-off wall.

A one-dimensional analytical model is proposed to analyze contaminant diffusion through a composite geomembrane cut-off wall (CGCW) composed of a geomembrane (GMB) and a bentonite cut-off wall (BCW). The model considers degradation process of contaminant and time-dependent inlet boundary condition which are common in engineering practices. Moreover, two limiting scenarios of the exit boundary condition (EBC) of CGCW for field conditions are taken into account, including the flushing and non-advective semi-infinite aquifer EBCs. The influence of boundary conditions and performance of CGCW are comprehensively investigated. The results show that the upper and lower limits of the mass flux of the exit face of CGCW can be obtained by the models with flushing EBC and the model with non-advective semi-infinite aquifer EBC, respectively. In addition, degradation has substantial influence on the contaminant migration, and smaller half-life in BCW results in smaller contaminant leakage. The performance of CGCW can be improved by embedding GMB at a proper location which is related to the type of contaminant and EBC. Furthermore, thickening HDPE GMB or adopting a coextruded EVOH GMB is efficient to improve the performance of CGCW. The present model can be used as an applicable tool for rational design of CGCW.

Ten-Year Experience in the Prevention of Post-Kasai Cholangitis.

BACKGROUND: Cholangitis is the most common complication after the Kasai procedure. It can be life-threatening and may affect long- and short-term outcomes of children with biliary atresia. We summarize our experiences in the prevention of early-onset cholangitis. PATIENTS AND METHODS: From January 2002 to March 2013, children with biliary atresia (BA) who underwent the Kasai procedure in the General Surgical Department were included in a retrospective cohort study. These patients were divided into group A (therapy 1) and group B (therapy 2) depending on the infection prevention protocol and occurrences of cholangitis within the six months after surgery were recorded. Two hundred eighteen children were included in this cohort study. Seventy-six children (35 females and 41 males) were included in group A. One hundred forty-two children (65 females and 77 males) were included in group B. Therapy 1 was our primary protocol and included a third-generation cephalosporin, metronidazole, and human immunoglobulin. Therapy 2 was a modification of therapy 1 that involved imipenem-cilastatin and human immunoglobulin. Statistical analyses were performed. A p value below 0.05 was regarded as significant. RESULTS: In group A, 45 children developed cholangitis within the six months after the Kasai procedure. In group B, 14 of these children experienced post-operative cholangitis. A χ2 analysis was used to examine the difference in the incidence of cholangitis between groups A and B. There was a substantial difference in the morbidity of post-operative cholangitis between groups A and B (59.2% vs. 9.9%, p = 0.000). CONCLUSION: Cholangitis in the early period after a Kasai procedure can be prevented effectively with an advanced prophylactic protocol.

STROBE-anastomotic leakage after pull-through procedure for Hirschsprung disease.

This study was undertaken to explore the causes, diagnosis, and treatment of anastomotic leakage after pull-through (PT) procedure for Hirschsprung disease (HD).A retrospective analysis of patients with anastomotic leakage after a PT procedure in the General Surgery Department of Beijing Children's Hospital from July 2013 to June 2016 was undertaken. The surgical characteristics, diagnosis, and treatment were retrospectively analyzed.Among the 213 patients who underwent PT procedures, 5 patients had a documented anastomotic leakage. The median age of these 5 patients at the time of the PT procedure was 6.8 years old, and this was higher than those without anastomotic leakage (1.7 years old). In all patients, rectal examination in the lithotomy position revealed an anastomotic dehiscence at the 6 o'clock position. The abdominal ultrasonography demonstrated retrorectal pneumatosis with or without an abscess in 4 patients. All patients were treated with ileostomies and anastomotic resuturing. The median delay to management was 4 days (range: 1-29 days). Four patients (4/5, 80%) were cured, and 1 (delay, 29 days) of these 4 patients developed postoperative ileus. The remaining patient (delay, 9 days) was required to undergo a repeat PT procedure. For the 4 cured patients, the median follow-up time was 20 months (range: 15-37 months), and these patients defecated 3 times daily at most without soiling.Older children with HD might be prone to anastomotic leakage. The findings of the rectal examination and ultrasonography were distinctive and useful for the diagnosis. Early ileostomy and resuturing of the anastomosis could be used to treat anastomotic leakage.

Assessment of liver fibrosis by Fibroscan as compared to liver biopsy in biliary atresia.

AIM: To evaluate liver stiffness measurement (LSM) using non-invasive transient elastography (Fibroscan) in comparison with liver biopsy for assessment of liver fibrosis in children with biliary atresia (BA). METHODS: Thirty-one children with BA admitted to the Department of Pediatric Surgery of Beijing Children's Hospital from March 2012 to February 2013 were included in this study. Their preoperative LSM, liver biopsy findings, and laboratory results were studied retrospectively. RESULTS: The grade of liver fibrosis in all 31 patients was evaluated according to the METAVIR scoring system, which showed that 4 cases were in group F2, 20 in group F3 and 7 in group F4. There were 24 non-cirrhosis cases (F2-F3) and 7 cirrhosis cases (F4). In groups F2, F3 and F4, the mean LSM was 9.10 ± 3.30 kPa, 11.02 ± 3.31 kPa and 22.86 ± 12.43 kPa, respectively. LSM was statistically different between groups F2 and F4 (P = 0.002), and between groups F3 and F4 (P = 0.000), however, there was no statistical difference between groups F2 and F3 (P = 0.593). The area under the receiver operating characteristic curve of LSM for ≥ F4 was 0.866. The cut-off value of LSM was 15.15 kPa for ≥ F4, with a sensitivity, specificity, positive predictive value and negative predictive value of 0.857, 0.917, 0.750 and 0.957, respectively. CONCLUSION: Fibroscan can be used as a non-invasive technique to assess liver fibrosis in children with BA. The cut-off value of LSM (15.15 kPa) can distinguish cirrhotic patients from non-cirrhotic patients.

Anterior perineal fistulectomy in repairing H-type rectovestibular fistula with a normal anus in female children.

The purpose of this study was to review a 7-year operative experience of anterior perineal fistulectomy in repairing H-type rectovestibular fistula with a normal anus in female children. From January 2007 to December 2013, 105 female children with H-type rectovestibular fistula and a normal anus underwent anterior perineal fistulectomy in the Department of General Surgery, Beijing Children's Hospital, Capital Medical University. Clinical data were retrospectively analyzed. Patients' age ranged from 6 months to 13 years 10 months, with an average age 5 years 2 months. The clinical feature of this disease was a definite history of vestibular infection at about 30 days after birth and leakage of gas or loose stool through vestibular fistular orifice after the infection was controlled. All patients had a normal anus. Follow-up through telephone or outpatient visits from 6 months to 7 years (median, 5.2 years), showed that all the patients were continent and had regular bowel movements. Among the 105 patients, 97 (92.4%) gained primary healing with a satisfactory appearance; 8 (7.6%) patients relapsed, among which 5 healed after hip bathing treatment within 3 weeks, 2 required another anterior perineal fistulectomy 7 months later and were cured, and the last one had another anterior perineal fistulectomy 1 year 10 months later but relapsed again, which healed after hip bathing treatment within 3weeks after the second surgery. Anterior perineal fistulectomy is a simple, safe and reliable surgical method to treat H-type rectovestibular fistula with a normal anus.