ABSTRACT
The demand for energy has been growing over the years to match development and population growth. The current sustainable development model advocates for the use of renewable (green) energy sources with an aim of lowering carbon emissions thereby mitigating the effects of climate change. A circular economy aspires to keep materials in use for as long as possible thus the reuse of agricultural waste especially in energy generation is a step in this direction. This study reports on the optimization of anaerobic digestion parameters for biogas production when wastes from pineapple are co-digested with those from livestock. The volume of biogas yield was optimized with regards to temperature, pH value, and mixing ratio of the substrates using Box Behnken Design (BBD), a class of Response Surface Methodology (RSM). This was achieved through a software package, Design Expert 13.The experiments were performed using Rehau home gas systems of 6 m3 in Jomo Kenyatta University of Agriculture and Technology. Pineapple wastes were co-digested with livestock waste in the ratio of 1:1, 1:2 and 1:3. The numerical optimization results revealed that the maximum biogas yield was 1.98 m3 when the pH was set at 6.0, temperature at 30 °C and pineapple mixing ratio at 62.5%. The results from this study can form a basis for policy makers in formulating strategies to guide adoption of biogas generated from agricultural waste as a key green energy for the economy.
ABSTRACT
BackgroundAccurate and timely diagnosis is essential in limiting the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Real-time reverse transcription-polymerase chain reaction (rRT-PCR), the reference standard, requires specialized laboratories, costly reagents, and a long turnaround time. Antigen rapid diagnostic tests (Ag RDTs) provide a feasible alternative to rRT-PCR since they are quick, relatively inexpensive, and do not require a laboratory. The WHO requires that Ag RDTs have a sensitivity [≥]80% and specificity [≥]97%. MethodsThis evaluation was conducted at 11 health facilities in Kenya between March and July 2021. We enrolled persons of any age with respiratory symptoms and asymptomatic contacts of confirmed COVID-19 cases. We collected demographic and clinical information and two nasopharyngeal specimens from each participant for Ag RDT testing and rRT-PCR. We calculated the diagnostic performance of the Panbio Ag RDT against the US Centers for Disease Control and Preventions (CDC) rRT-PCR test. ResultsWe evaluated the Ag RDT in 2,245 individuals where 551 (24.5%, 95% CI: 22.8-26.3%) tested positive by rRT-PCR. Overall sensitivity of the Ag RDT was 46.6% (95% CI: 42.4-50.9%), specificity 98.5% (95% CI: 97.8-99.0%), PPV 90.8% (95% CI: 86.8-93.9%) and NPV 85.0% (95% CI: 83.4-86.6%). Among symptomatic individuals, sensitivity was 60.6% (95% CI: 54.3-66.7%) and specificity was 98.1% (95% CI: 96.7-99.0%). Among asymptomatic individuals, sensitivity was 34.7% (95% CI 29.3-40.4%) and specificity was 98.7% (95% CI: 97.8-99.3%). In persons with onset of symptoms <5 days (594/876, 67.8%), sensitivity was 67.1% (95% CI: 59.2-74.3%), and 53.3% (95% CI: 40.0-66.3%) among those with onset of symptoms >7 days (157/876, 17.9%). The highest sensitivity was 87.0% (95% CI: 80.9-91.8%) in symptomatic individuals with cycle threshold (Ct) values [≤]30. ConclusionThe overall sensitivity and NPV of the Panbio Ag RDT were much lower than expected. The specificity of the Ag RDT was high and satisfactory; therefore, a positive result may not require confirmation by rRT-PCR. The kit may be useful as a rapid screening tool for only symptomatic patients in high-risk settings with limited access to RT-PCR. A negative result should be interpreted based on clinical and epidemiological information and may require retesting by rRT-PCR.
