Roles of survival situation and personality temperament in the relationship between life stress and depression of higher vocational college students.

BACKGROUND: Higher vocational college students face more life stress, which can easily result in depression and hinder their healthy growth. This study aimed to explore the roles of survival situation and personality temperament in the relationship between life stress and depression. METHODS: A self-compiled "College Students' Life Stress and Mental Health Questionnaire" was used to survey 4800 students in a Chinese higher vocational college. The questionnaire consisted of five subscales: life stressors scale, stress response scale, depression scale, personality temperament types scale, and survival situations scale. The sample included 4705 students, of whom 3449 (73.30%) were males and 1256 (26.70%) were females, with 990 urban students (21.04%), 3715 rural students (78.96%). The age of the participants ranged from 17 to 33 years. The data were analyzed using SPSS v26, PROCESS v3.3, and AMOS v23. RESULTS: (1) The depression rate of higher vocational students was 18.10% (with a severe depression rate of 1.60%). Life stress could explain 43.80% of depressive episodes (p < 0.01), (2) Among survival situations, the depression degree and rate of students in adversity were the highest (M = 1.56, 24.10%), (3) Among temperament types, the depression degree and rate of melancholic students were the highest (M = 2.13, 36.05%), (4) Survival situation and personality temperament had significant moderating interaction effects on depression caused by life stress (p < 0.01), students in adversity and depressive temperament were more susceptible, (5) Survival situations moderated three paths of the "life stressors-stress response-depression" partial mediation model, and personality temperament types moderated "stress response-depression" path. CONCLUSION: Prosperity and sanguine temperament are protective factors of depression caused by life stress in higher vocational students. Dilemma, adversity and melancholic temperament are risk factors of depression caused by life stress in higher vocational students.

Cation exchange resin pretreatment enhancing methane production from anaerobic digestion of waste activated sludge.

The application of anaerobic digestion (AD) to treat waste activated sludge (WAS) still exhibits some limitations, such as low methane production. In this study, cation exchange resin (CER) pretreatment was explored to enhance the efficiency of the AD of WAS. Based on the response surface methodology, the optimal conditions for CER pretreatment were reaction time of 7.4 h, 33.8 g CER (wet weight) /g volatile solids and sludge total solids of 2.4%. Under these optimal CER pretreatment conditions, approximately 30% of metals were removed from the WAS, particularly organic-binding metals. This metal removal disrupted the structures of extracellular polymer substances and led to sludge deflocculation, thereby releasing large amounts of organic substances from the sludge solids. Batch AD experiments showed that CER pretreatment increased the maximal production of volatile fatty acids and methane by 565.7% and 80.5%, respectively. Additionally, CER pretreatment promoted each stage of AD (i.e. solubilisation, hydrolysis, acidification and methanation) and the corresponding activities of key enzymes. Experimental results for semi-continuous AD further confirmed that CER pretreatment enhanced the proportion of methane in the biogas (from 62.75 ± 2.14% to 73.96 ± 0.99%) and the production of methane. An analysis of changes in the microbial communities demonstrated that CER pretreatment enhanced the abundance of microorganisms involved in hydrolysis, acidification and acetification and changed the major methanogenic pathway from acetoclastic methanogens to methylotrophic methanogens. These findings are expected to provide a reference for developing new pretreatment methods for enhancing anaerobic biodegradability of organic matters.

Enhancing short-term ethanol-type fermentation of waste activated sludge by adding saccharomycetes and the implications for bioenergy and resource recovery.

Ethanol-type sludge fermentation has recently attracted much attention because it can enhance direct interspecies electron transfer and thus improve the anaerobic digestion of waste activated sludge (WAS). In this paper, the enhancement of short-term ethanol-type fermentation of WAS via adding Saccharomyces was investigated. The experimental results show that the maximum ethanol production of 1030.8 ± 20.6 mg/L was achieved, with the optimum fermentation conditions of a pH of 5.1, temperature of 26.0 â„ƒ and time of 8.0 hr. Although the content of volatile fatty acid (VFA) increased within 10 hr, it is one order of magnitude lower than the content of ethanol, indicating that the VFA generation did not affect the efficient production of ethanol. The analyses of changes in the microbial community during the fermentation process demonstrate that the greatest Saccharomyces activity occurred in the first 8 hr and it can play an important role in ethanol production even at a very low relative abundance. Meanwhile, most typical acid-producing bacteria were inhibited, but the hydrogenotrophic methanogens (i.e., Methanobacterium) were enriched to a certain extent. Further statistical analyses reveal that the Rhodobacter, Thermomonas, Terrimonas and Saccharomyces are responsible for ethanol production during the fermentation. However, these findings not only provide a reference for the development of enhancing ethanol-type fermentation of sludge, but also are expected to provide a new way of thinking for the efficient bioenergy and resource recovery from sludge.

An overview of removing heavy metals from sewage sludge: Achievements and perspectives.

The removal of heavy metals from sewage sludge (SS) is attracting increasing attention because the presence of toxic heavy metals in SS restricts its reuse or disposal, especially on land. This review presents an overview of research on the origin and chemical speciation of heavy metals in SS and describes methods for their removal. SS primarily absorbs heavy metals from wastewater via passive sorption and active uptake of biomass, resulting in the different chemical speciation. The advantages and disadvantages of the current methods for the removal of heavy metals from SS are analysed. The current methods focus on the removal efficiencies of heavy metals, which are high enough to meet the standard of land application, but the treatment cost, the change and retention of nutrients, and the effects on SS properties resulting from heavy metal removal are usually ignored. In this review, the main knowledge gaps are identified and proposals for future research are made. These should comprise determining the underlying mechanisms of current removal methods, optimising and integrating the removal methods, and establishing systematic evaluation standards for these methods. This review will help researchers develop new environmentally and economically friendly methods for the removal of heavy metals from SS.

Enhancing acidogenic fermentation of waste activated sludge via isoelectric-point pretreatment: Insights from physical structure and interfacial thermodynamics.

The poor biodegradability of waste activated sludge (WAS) is widely regarded as one of the main bottlenecks in the fermentation of sludge and is attributed mainly to the complex nature of sludge. In this study, the physical structure and interfacial thermodynamics of sludge, which reflect its complex nature, were explored to reveal the effects of isoelectric-point (pI) pretreatment on enhancing the production of volatile fatty acids (VFA). It was observed that the maximum VFA production and the initial VFA production rate increased by 151.2% and 46.6%, respectively, after pI pretreatment, which indicates that pI pretreatment significantly improved the generation efficiency of VFA. The experimental results of 12-day acidogenic fermentation assays following pI pretreatment show that the maximum concentrations of soluble total organic carbon, soluble protein and soluble polysaccharide increased by 209.8%, 148.9% and 84.5%, respectively, and the maximal proportion of low molecular weight (<1 kDa) soluble organic substances increased by 92.4%, thus confirming that pI pretreatment can promote organic solubilisation and hydrolysis in sludge. The analyses of changes in the fractal dimension (Df), the spatial configuration of extracellular polymeric substances, and the interfacial non-covalent interaction energy of sludge during the fermentation process reveal that pI pretreatment can loosen the physical structure, promote the spatial extension of biopolymer molecular chains, and increase the driving forces of solid-liquid interfacial enzymatic reactions. It is thus hypothesised that these changes could be responsible for the high degree of organic solubilisation, hydrolysis and acidification of WAS, which is further confirmed by correlation analyses of the Df and interfacial free energy versus VFA production. These findings are expected to provide a possible means to improve the biodegradability of sludge via its pI to trigger dismantling of the sludge structure and increase the driving forces of interfacial enzymatic reactions.

Effects of humic matter on the anaerobic digestion of sewage sludge: New insights from sludge structure.

A sludge structure perspective of the effects of humic matter (HM) on the anaerobic digestion (AD) of sewage sludge was proposed and investigated in this study. It was observed that the net cumulative methane production of sludge was significantly lower in the presence of HM. The fractal dimension values of sludge samples were increased by the addition of HM, whilst their total surface energy values were decreased, indicating that HM reinforced the stability of the sludge structure. Analyses of the physicochemical properties of different sludge samples revealed that HM enhanced the structural stability of sludge organic substances and restricted its organic solubility by interacting with the biopolymers to form a dense granular aggregate, thereby reducing the random-coil degree of extracellular organic substances and its active sites for enzymes, which suggested that HM could inhibit AD by changing the sludge structure. It was further confirmed by the biochemical methane potential (BMP) assay process. The BMP tests and corresponding kinetic analyses revealed that HM can restrict the potentials of sludge organic solubilisation, hydrolysis and acidification processes, but not necessarily the rates of these processes by enhancing the structural stability of high molecular weight readily biodegradable organic matter (RBOM) and restricting the mobility of low molecular weight RBOM (i.e., hydrolysis products). These findings can enrich understanding of the AD of sludge and may thus aid in the development of more effective methods to improve sludge treatment.

Perspective on enhancing the anaerobic digestion of waste activated sludge.

Anaerobic digestion (AD) of waste activated sludge (WAS) is an important bio-energy strategy that has been hindered by low conversion efficiency. This paper presents a comprehensive review of research on the sludge's property and enhancing AD of WAS, and proposes two perspectives of material structure and microbial activity on improving AD efficiency. In the first part of this review, the key principle problems for hindering AD efficiency are identified based on the concept of AD. Then, the possibility that the complex microstructure and composition of WAS are responsible for poor biodegradability is considered and main methods for enhancing AD are summarized. In the third part, according to the published works, the main knowledge gaps in research are recognized as the identification and specific activity adjustment of functional microbes, the understanding of key constituents of WAS and their interactions, the deciphering of complex structure of sludge organic substance, and the revealing of relationships between complex nature of WAS and biodegradability. Further discussions reveal that to enhance AD more studies should be centered on the sludge's structure and properties in future. However, this review is expected to provide the clear and accurate research directions for enhancing AD efficiency of WAS.