Fate of Functional Bacterial and Eukaryotic Community Regulated by Earthworms during Vermicomposting of Dewatered Sludge, Studies Based on the 16S rDNA and 18S rDNA Sequencing of Active Cells

DNA sequencing of active cells involved in vermicomposting can clarify the roles of earthworms in regulating functional microorganisms. This study aimed to investigate the effect of earthworms on functional microbial communities in sludge by comparing biodegradation treatments with and without earthworms. PCR and high throughput sequencing based on pretreatment of propidium monoazide (PMA) were used to detect the changes in active bacterial 16S rDNA and eukaryotic 18S rDNA during vermicomposting. The results showed that the nitrate in sludge vermicomposting and control were significantly different from day 10, with a more stable product at day 30 of vermicomposting. Compared with the control, the Shannon indexes of active bacteria and eukaryotes decreased by 1.9% and 31.1%, respectively, in sludge vermicompost. Moreover, Proteobacteria (36.2%), Actinobacteria (25.6%), and eukaryotic Cryptomycota (80.3%) were activated in the sludge vermicompost. In contrast, the control had Proteobacteria (44.8%), Bacteroidetes (14.2%), Cryptomycota (50.00%), and Arthropoda (36.59%). Network analysis showed that environmental factors had different correlations between active bacterial and eukaryotic community structures. This study suggests that earthworms can decrease the diversity of bacterial and eukaryotic communities, forming a specific-functional microbial community and thus accelerating organic matter decomposition during vermicomposting of dewatered sludge.

Integral Assessment of Organic Fertilization on a Camelina sativa Rotation under Mediterranean Conditions

The goal of this study was to provide quantitative agronomic data and environmental performance through a life cycle assessment of camelina in a crop rotation. For this purpose, camelina [Camelina sativa (L.) Crantz] was included in a crop rotation (camelina-barley [Hordeum vulgare (L.)]-camelina) fertilized with two organic fertilizers (dewatered sludge and composted sludge) during three growing seasons (2015–2018). Three treatments were considered in this experimental study of 0.018 ha: (1) Fertilization with composted sludge (15 t ha−1), (2) fertilization with dewatered sludge (35 t ha−1), and (3) control treatment without fertilization. Results showed that camelina’s yield was affected by climatic conditions, ranging from 0.9 to 1.4 t ha−1 in the first season (2015/2016) and the third season (2017/2018 and did not present significant differences between treatments. The yield components with a positive response to organic fertilization were number of silicles, number of seeds per plant, and thousand-seed weight, with an average increase compared to the control of 23.7%, 16.5%, and 18.5%, respectively. A negative correlation was observed between organic fertilization and total fat content, contrary to the increase in protein content observed with organic fertilization. The environmental assessment of this crop rotation revealed that fertilization and transport were the main hotspots. Despite the undesirable weather limitations, this study showed a positive response of camelina’s yield components and seed quality to organic fertilization. By applying these organic fertilizers, it may be possible to obtain favorable camelina yields and promote waste valorization. To minimize the environmental impacts of this crop rotation with camelina, the main recommendations could be to reduce the distances between the dewatering and composting sites and the field and optimize fertilization rates. Further research is needed to determine the application of these organic fertilizers in the long term.

Comparative Study of Hot Air Drying and Microwave Drying for Dewatered Sludge

Large amounts of sludge are generated from wastewater treatment in seafood processing industries. Most of the dewatered sludge in Thailand is not utilized and disposed by landfilling. The dried sludge utilization as refuse-derived fuel (RDF) is an alternative solution due to the gross calorific value (GCV), which is greater than 21.9 MJ/kg. However, the key obstacle is its high moisture content of 87.4% (wet basis). Therefore, drying methods using hot air and microwave techniques were investigated for preparing dried sludge. The effects of hot air temperatures (100-150 °C) and microwave power levels (100-800 W) were compared on drying kinetics, specific energy consumption (SEC), and characteristics of the dried products. The results showed that drying times were decreased by increasing the hot air temperatures. In the same way, the increase in microwave power levels decreased the drying time. The application of microwaves contributed to reducing the drying time by more than 46% compared to the hot air. The reduction of drying times resulted in the saving SEC. The GCV of the dried sludge decreased with the decrease in the volatile matter (VM) due to the high component of VM as 79.5-80.3% (dry ash-free basis). The sludge dried by the microwaves showed a lower GCV than the hot air products. However, dried sludges still had high GCV (≥ 20.8 MJ/kg). Furthermore, the minimal variation of the product characteristics demonstrated that the microwave technique could be applied as an alternative drying method with a rapid process compared to the conventional hot air technique.