Receiving external dewatered sludge cakes at a centralised anaerobic digester is an interesting option to maximise resource recoveries at the site. The study classified the organic particulates of dewatered sludge cakes into three types based on each kinetic property in the anaerobic digestion. The hydrolysis of the type-I compound having a Contois-type reaction was sensitive to the acidogen concentration, whilst the type-II compound had as high as 10 times the first-order reaction rate of the heterotrophs Eanaerobic decay. A part of the type-I and type-II compounds was speculated to be derivatives of the already-disintegrated heterotrophic biomass in the sludge dewatering process. The type-III compound was physically fragmented in forming acidogenic substrates, creating a peak of methane production rate in the batch operations. The mathematical simulations based on the 16 dewatered sludge cake samples indicated a continuous digester at a retention time of 20 E0 d would yield biogas with a COD-based methane conversion efficiency of 53% when a dewatered sludge cake was fed. Due to the high hydrolysis kinetics of the type-II compound, the process performance of the digester was supposed to be 4% higher than that receiving the mixture of primary sludge and waste activated sludge.
Over the past decade, water hyacinth infestation has posed a serious threat to Lake Tana, the largest lake in Ethiopia. During the rainy seasons, the infested area can expand to nearly 30 km2 along the shoreline, causing severe impacts on human activities and local ecosystem. In this study, we collected satellite imagery from 2015 to 2025 and analyzed the long-term variation in water hyacinth coverage in Lake Tana to assess the potential factors influencing its population dynamics and to promote effective weed management strategies. Our results indicate that lake water level is a critical driver of water hyacinth infestation in Lake Tana. By expanding the riparian zones suitable for water hyacinth proliferation, elevated water levels lead to larger coverage regardless of the season. We also evaluated various removal strategies and found that current harvesting practices conducted during the rainy season are relatively ineffective. Targeting the weeds before their rapid expansion, i.e., prior to the rainy season, is likely to achieve more effective suppression. When combined with other lake management measures, such as reducing nutrient inputs, such strategies could progressively reduce water hyacinth infestation and mitigate its ecological and socioeconomic impacts.
High seafood consumption may increase exposure to heavy metals and thereby pose risks to human health. Therefore, twenty five samples of each yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis) were collected from major fishery harbours of Sri Lanka between January and August 2024. Fourteen trace metals were investigated using inductively coupled plasma mass spectroscopy (ICP-MS) aiming at updated monitoring of trace metal levels. A risk assessment made on the individual target hazard quotient (THQ) indicated that all concentrations of metals, except for mercury (Hg) in T. albacares, were below 1, revealing negligible non-carcinogenic health concerns. The target cancer risk (TR) values for inorganic arsenic (iAs), and chromium (Cr) were below the 10∁E, showing no carcinogenic risks associated with long-term consumption of tuna. The Se:Hg molar ratios exceeded one for both fish species. Positive selenium health benefit values (HBVSe) were observed in both fish species, indicating their positive contribution to improving the Se status of the consumer while mitigating the toxic effects of Hg. The study emphasizes the dual role of fish as both a nutrient source and a vector for contaminant exposure, emphasizing the need for ongoing monitoring of metal contamination in marine organisms.
A convenient, straightforward method was developed for measuring sediment oxygen demand (SOD) rates using disturbed sediment samples. A disturbed sediment sample was placed in a ~400 mL glass vessel equipped with four oxygen sensors and adjusted to a thickness of approximately 1 cm. Oxygen-saturated artificial seawater was added and sealed. Dissolved oxygen (DO) was measured using a fibre-optic oxygen meter, and the SOD rate was calculated from the changes in DO over time. The SOD rate calculated from the middle layer of DO closely corresponded (approximately 1:1) with the rate calculated from the weighted average of DO measured across the four layers, despite the non-stirring system used. This indicated that a single DO measurement in the middle layer was sufficient to calculate the SOD rate using this method. The SOD rates measured using this method were higher in the inner bay than at other sites, consistent with previously reported spatial trends, suggesting that this method effectively captures the spatial variation in SOD rates. Overall, this approach is well-suited for investigating the horizontal distribution and long-term monitoring of the SOD rate, potentially facilitating the accumulation of SOD rate data and improving water quality.
Shallow wells are common source of drinking water in low-resource countries; however, they are highly vulnerable to fecal contamination. Here, we assessed the microbial quality and antibiotic susceptibility patterns of enteric bacteria recovered from shallow wells situated near sanitation facilities in four security-challenged areas of Katsina State, Nigeria. A total of 45 water samples were collected from 15 wells. Bacterial isolation and identification were performed using standard microbiological procedures and the analytical profile index (API) 20E kit. Antibiotic susceptibility testing was performed using the disk diffusion method, and Pearson’s correlation was performed to determine associations between risk factors and microbial contamination. Total coliform counts exceeded the World Health Organization-recommended limits. Klebsiella pneumoniae (25.0%) was the most frequently isolated species, followed by Salmonella species (20.83%) and Escherichia coli (16.67%). Notably, 86.5% of isolates exhibited multidrug-resistant phenotypes. Well distance relative to sanitation structures did not establish a causal relationship between sanitary risk scores and total coliform counts (r = 0.32, p = 0.47). Improved sanitation, regular water disinfection, and routine surveillance of groundwater is recommended to protect vulnerable communities in these security-challenged areas. A limitation of this study is its relatively small sample size and reliance on phenotypic methods, which may limit the comprehensiveness of the analyses.
