Assessing the Efficacy of Dissolved Ferric Chloride Conditioner on Dewaterability of Sewage Sludge

The aim of this study was to investigate the efficacy of dissolved ferric chloride conditioner on dewaterability of sewage sludge. A funnel- shaped drying bed of 420mm surface diameter, 340mm vertical depth, 25mm diameter discharge pipe was used in this study, and containing 75mm thick sand layer, grain size 0.20mm – 0.60mm diameter. On this layer was placed 200mm thick sewage sludge thoroughly mixed with ferric chloride solution, introduced into the drying bed and filtration allowed to take place. Discharge from the control experiment was further and faster with maximum discharge of 201m3 at the 400th minute. Repeating the experiment on the 2nd, 3rd, 4th, 5th and 6th days, maximum discharges of  78cm3, 41 cm3, 40 cm3 , 39 cm3 and 39 cm3 were experienced at the 300th minute for the 2nd day, 200th, minute for the 3rd and 4th days and 180th minute for the 5th and 6th days respectively. Efficacy retardation factors were 2.577, 4.902, 5.025, 5.154, 5.154 for the 2nd, 3rd, 4th, 5th and 6th days. Minimum and maximum instantaneous inhibition coefficients were found to be 0.52 and 0.78 which indicates high inhibition. The result of specific resistance to filtration  show that it increased tremendously when the salt is stored in solution. Specific resistance to filtration are , , , ,  and  in the 1st, 2nd, 3rd, 4th, 5th and 6th days respectively. There was no consistent increase in these values, but seem to be fluctuating. This anomalous behaviour is a limitation in the work of  Ademiluyi and Arimieari, and because of that, their model is not so good in the prediction of specific resistance to filtration.http://dx.doi.org/10.4314/njt.v34i2.2

A Study of Faecal Coliform Die-Off in Sewage Sludge Drying Bed

The aim of this study was to assess the interacting characteristics of sewage sludge such as temperature, pH, and moisture content of sludge at defined time intervals as to how they affect Coliform die-off in a drying bed. Samples were collected at 0.0mm depth (i.e. surface of sludge), 60mm, 120mm, 180mm and 240mm, and colony count tests were performed on the samples. Results indicate that the number of Coliforms was minimum at the surface, maximum at 60mm depth, and decreased consistently to another minimum value at 240mm depth. This trend could be as a result of the organisms being in their exponential phase with adequate nutrients and growth conditions at 60mm depth, which later experienced decrease in available nutrients, oxygen and unfavorable growth conditions such as unfavorable temperatures, reduced moisture content, acidic pH and water activity. Range of the maxima and minima values of CFU/100ml for the five horizons considered over a period of 76 days were This finding does not conform with the work of Al Malack and others [6] because from their results, the various pathogenic organisms studied were found to survive longer as the sludge initial depth was increased. Short-term and long-term effect of drying indicate that low moisture content favours microbial decay because pathogen removal rate was consistently increasing from 21/01/2013 to 08/02/3013, a condition which started prevailing when the moisture content of sludge in the drying bed had decreased from 88.99 per cent on 29/11/2012 to 65.48 per cent on 21/01/2013. It was recommended that conditioners should be used to dewater sludge faster in order to speed-up pathogen die-off rate in drying beds.http://dx.doi.org/10.4314/njt.v34i3.3

Effect of Conditioner on Dewaterability of Sewage Sludge

A model for dewaterability of conditioned sludge was derived based on data generated after dewaterability experiments using six sand drying beds. In these experiments, Six beds were used, the first bed contain no conditioner and served as control experiment. Ferric Chloride was added to the remaining five beds in the neighborhood of 1%, 2%, 3%, 4%, and 5% respectively, corresponding to 30g, 60g, 90g, 120g, and 150g of FeCl3 Seepage (sg) was derived as a linear function of time. The coefficient of correlation obtained from the linear regression of seepage against time corresponding to 30g, 60g, 90g, 120g and 150g are 0.860, 0.844, 0.781, 0.722 and 0.535 respectively. Moisture content of sludge was 86.69% when no coagulant was added, it was 69.47%, 57.32%, 54.01%, 52.79% and 47.81% when 30g, 60g, 90g, 120g and 150g doses were used with a range of 38.88%. Dewaterability enhancement ratio was 1:1 for control experiment, 1:27.72, 1:46.59, 1:51.72, 1:53.62 and 1:61.34 for 30g, 60g, 90g, 120g, and 150g doses respectively. Statistical test parameter, bp-valueb was computed for each coagulant dose and hypothesis tested at 95% level of significance. The bp-valueb results corresponding to 30g, 60g, 90g, 120g and 150g are 0.000, 0.001, 0.003, 0.008 and 0.073. Based on the decision rule, it was concluded that the model is adequate. This modelB is good, but its deficiency lies in the fact that the coefficient of correlation between measured and calculated quantities of seepage at specified coagulant doses decrease with increase in coagulant dosage. Though, the higher the quantity of coagulant used, the higher the dewaterability ofB sewage sludge which is a big plus. The disadvantage of using coagulants in dewatering sludge lies in the fact that the effluent cannot be recycled for consumption because of the toxic Ferric Chloride that has been used as conditioner. It is recommended that further research be carried out to improve on this already existing model.http://dx.doi.org/10.4314/njt.v33i3.2

Modeling of Seepage Losses in Sewage Sludge Drying Bed

This research was carried out to develop a model governing seepage losses in sewage sludge drying bed. The model will assist in the design of sludge drying beds for effective management of wastes derived from households’ septic systems. In the experiment conducted this study, 125kg of sewage sludge, 90.7% moisture content was thoroughly mixed and intermittently into a sand drying bed of dimensions 1.0m length, 0.3m width, 0.8m depth including overboard and having a 50mm diameter drain pipe. Seepage were measured at 24 hours intervals for 15 days, after which seepage model was derived from first principles based on the concept that seepage is inversely proportional to time. The model is in the form and for this model, two cases exist, cases I and II respectively. For case I, as time, tends to infinity (i.e. t →∞) at which point seepage has completely stopped (i.e qs=0) and the seepage curve intercepts the x-axis so that the intercept a = 0, data generated was modeled first by calibration using odd number values of seepage corresponding to 1 to 15 days. Coefficient of correlation after calibration was found to be r=-0.8474, and after verification using even number values of seepage corresponding to 2 to 14days, r =0.8474 was the coefficient of correlation between measured and calculated quantities of seepage which validates the model. For seepage model case II, this was at the initial stage of application of sludge into the drying bed at which point seepage was still taking place so that the intercept , then ‘a’ was determined by trial and error. Again, calibration and verification was done as in case I and correlation of measured and calculated seepage gave r=0.972, this high value of ‘r’ validates the model.http://dx.doi.org/10.4314/njt.v34i1.

Modeling of Evaporation Losses in Sewage Sludge Drying Bed

A model for evaporation losses in sewage sludge drying bed was derived from first principles. This model was developed based on the reasoning that the rate at which evaporation is taking place is directly proportional to the instantaneous quantity of water in the sludge. The aim of this work was to develop a model to assist in the design of drying beds for effective treatment of wastes derived from households’ septic systems.  Data generated after evaporation experiment in sewage sludge drying bed over a period of 15 days at 24 hours intervals was used for the modeling. The model was calibrated and regressed using data for days 1 to 8 by employing the Pearson’s correlation coefficient, “ ” was found to be -0.96124, after which verification was done and regressed using data for days 9 to 15 and  was found to be 0.9969 that these fits validates the model. Materials balance show that evaporation reduces with increase in seepage losses which can be enhanced with use of conditioners and coarser sands because of their larger pore spaces. It was discovered that evaporation from the sludge follows first order kinetic in agreement with the fundamental concept. The model will help in the prediction of total water losses due to evaporation over a given period which would aid in the design of drying beds.http://dx.doi.org/10.4314/njt.v34i4.3

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030