Coagulation is a well-known technology applied in water and wastewater treatment. Inorganic salts, such as alum, ferrous sulfate, and polyaluminum chloride, are usually used. It is widely known that utilization of these inorganic coagulants poses several disadvantages, such as high coagulant cost and high sludge volume that increase water treatment expenses. The use of alum also poses health risk to human as it may cause degenerative diseases. In order to minimize these disadvantages, the use of various coagulants from natural resources has been recently proposed. In this research, study was performed on the extraction and use of a potential natural coagulant (Leucaena leucocephala) seed kernel as natural coagulant. Leucaena seed kernel was extracted at various NaCl concentrations (0-5 mol L −1). Extract with highest protein content obtained at NaCl concentration of 3 mol L −1 was further used to treat a synthetic wastewater model substance (Congo red solution) at various pH (2-10) and dosage (2-40 mL L −1). This natural coagulant successfully removed 99.9% of the color at pH 3 and dosage 10 mL L −1 , with only half sludge volume discharged when compared to alum. The result suggests that leucaena is a promising natural coagulant for water and wastewater treatment.
Purpose
Furthermore, the purpose of this study is to compare the student engagement and the learning outcomes in offline and online PBL in the aforementioned course. The COVID-19 pandemic has caused disruption in various sectors, including education. Since it was first announced in mid-March 2020 in Indonesia, teaching and learning activities have been carried out online. In this study, a comparison of the offline (Spring 2019, prior to the pandemic) and online (Spring 2021, during the pandemic) problem-based learning (PBL) method in the sustainable chemical industry course is investigated.
Design/methodology/approach
A quantitative analysis was conducted by measuring the students’ engagement, course-learning outcomes (CLOs) and student learning outcomes (SLOs). Difference tests of engagement score, CLOs and SLOs were investigated by using the t-test or Mann–Whitney U-test. Furthermore, the perceived students’ stressors were measured.
Findings
It is found that the students’ engagement in offline and online PBL gives similar scores with no significant difference. This is possible because of the PBL structure that demands students to be actively engaged in gaining knowledge, collaboratively working in teams and interacting with other students and lecturers. Although similarly engaged, the CLOs and SLOs of online PBL are significantly lower than offline PBL, except for SLO related to oral and written communication skills and affective aspect. The decrease in CLOs and SLOs could be influenced by students’ academic, psychological and health-related stressors during the COVID-19 pandemic time.
Originality/value
This study provides a recommendation to apply online PBL during the COVID-19 pandemic time and beyond, although some efforts to improve CLOs and SLOs are needed.
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