Effect of enzymatic pre-treatment on thermophilic composting of shrimp pond sludge to improve ammonia recovery

Research Progress on Microbial Nitrogen Conservation Technology and Mechanism of Microorganisms in Aerobic Composting

With economic development and improvements in living standards, the demand for livestock products has steadily increased, resulting in the generation of large amounts of livestock manure, which seriously pollutes the ecological environment and poses a threat to human health. High-temperature aerobic composting is an effective method for treating livestock manure; however, traditional composting processes often lead to considerable nitrogen loss, reduced efficiency of soil conditioners, and increased emissions of harmful gases. The incorporation of physical, chemical, and biological additives can effectively retain nitrogen within the compost. Among these, microbial agents are particularly noteworthy as they precisely regulate the microbial community structure associated with nitrogen transformation during aerobic composting, altering the abundance of functional genes and enzyme activities involved in nitrogen transformation. This approach significantly reduces nitrogen loss and harmful gas emissions. This paper reviews the application effects of microbial agents on nitrogen retention during aerobic composting and explores the underlying regulatory mechanisms, aiming to provide theoretical guidance and new research directions for the application of microbial agents in enhancing nitrogen retention during aerobic composting.

Integrated nutrient recycling: Ammonia recovery from thermophilic composting of shrimp aquaculture sludge via self-heated bench-scale reactor and mango plant growth enhancement by the compost

Due to the rapid growth of the aquaculture industry, large amounts of organic waste are released into nature and polluted the environment. Traditional organic waste treatment such as composting is a time-consuming process that retains the ammonia (NH3) in the compost, and the compost produced has little economic value as organic fertilizer. Illegal direct discharge into the environment is therefore widespread. This study investigates the recovery of NH3 through thermophilic composting of shrimp aquaculture sludge (SAS) and its application as a soil conditioner for the growth of mango plants. A maximum composting temperature of 57.10 °C was achieved through self-heating in a 200 L bench-scale reactor, resulting in NH3 recovery of 224.04 mol/ton-ds after 14 days. The addition of calcium hydroxide and increased aeration have been shown to increase NH3 volatilization. The recovered NH3 up to 3 kg-N can be used as a source of clean nitrogen for high-value microalgae cultivation, with a theoretical yield of up to 34.85 kg-algae of microalgae biomass from 1 ton-ds of SAS composting. Despite the high salinity, SAS compost improved mango plant growth and disease resistance. These results highlight the potential of SAS compost as a sustainable source of clean nitrogen for microalgae cultivation and soil conditioner, contributing to a waste-free circular economy through nutrient recycling and sustainable agriculture.

Dissolved organic compounds in shale gas extraction flowback water as principal disturbance factors of soil nitrogen dynamics

Flowback water, a by-product of shale gas extraction, represents an extremely complex industrial wastewater characterized by high organic compounds content and high salinity. The prospect of flowback water entering the soil through various approaches concerns regarding its ecological risk. Nitrogen mineralization (Nmin), a key rate-limiting step in the soil N cycle, might be adversely affected by flowback water. Nonetheless, no previous studies have examined the effects of flowback water on soil Nmin rates, let alone quantified the relative contributions of the major components of flowback water to changes in Nmin rates. Therefore, this study investigated the effects of flowback water and sterile flowback water at two different concentrations on the Nmin rates of three distinct soil types. This study aimed to elucidate the predominant influence of the key constituents within flowback water on the changes in soil Nmin rates. The results showed that soil soluble salt content, dissolved organic carbon (DOC) and dissolved nitrogen (DN) content significantly increased by 8.37 times, 9.5 % and 26.4 %, respectively, in soils contaminated by flowback water. In comparison with the control group, the introduction of flowback water resulted in a significant 25.9 % reduction in Nmin rate in sandy soils. Conversely, in clay and loam soils, there was a significant increase in Nmin rates by 44.9 % and 131.8 % respectively. Throughout the incubation period, leucine-aminopeptidase activity exhibited irregular fluctuations. Analysis of microbial communities demonstrated that flowback water only significant impacted soil rare microbial taxa, inducing a significant increase in alpha diversity for sandy, clay, and loamy soils by -16.9 %, 10.12 %, and 1.63 %, respectively. Linear regression and random forest analyses indicated that alterations in soil DOC:DN ratio and salt content were responsible for changes in soil Nmin rates within flowback water-contaminated soils. In contrast, only salt content significantly contributed to shifts in alpha diversity among soil rare microbial taxa. Structural equation modeling highlighted that the total effect of dissolved organic compounds (DOC and DN, λ = 0.64) from flowback water was greater than the total effect of salinity (λ = 0.24) on soil Nmin rates. In conclusion, our findings imply that dissolved organic compounds within flowback water play pivotal roles in determining soil Nmin rates. To the best of our knowledge, this is the first study to reveal the effects of major components in the flowback water on soil N mineralization rates.

Hydrothermal liquefaction of municipal sludge and its products applications

Hydrothermal liquefaction (HTL) is an effective medium-temperature, high-pressure thermochemical process to dispose municipal sludge (MS), and biocrude (a crude bio-oil) is its main product. Many efforts are continued extensively to improve conversion efficiency and to promote industrial application of this technology. This work focuses on critical influencing factors (e.g., reaction temperature, residence time, atmosphere, solvent, catalyst, and pretreatment) and fundamental transformation mechanisms of main components (i.e., lipids, proteins, and carbohydrates) in MS HTL. It also analyzes migration behavior of heavy metals during MS HTL, which can provide a reference for subsequent recovery of nutrients from HTL products. Moreover, the applications of MS HTL products are systematically expounded, and potential challenges and opportunities are highlighted as well. It is necessary to develop advanced methods of catalyst recovery and innovative biocrude upgrading methods so as to reduce HTL investment and operating costs. Reusing aqueous phase and solid phase products as reaction medium and catalyst carrier separately after MS HTL is feasible to realize resource utilization of MS. This information can provide valuable guidance to promote MS HTL industrialization.

Effect of the addition of biochar and wood vinegar on the morphology of heavy metals in composts

In the experiment, the morphology of heavy metals (Pb, Cr, Cd, and Ni, HMs) was characterized using flame atomic absorption spectroscopy. In addition, Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) were used to characterize the correlation between environmental factors and metal morphology in the rotting compost from several angles. The results showed that the humus treated with wood vinegar solution had a high degree of humification and rich aromatic structure. FTIR spectroscopy confirmed that the degree of humus aromatization gradually increased during the composting process, which enhanced the complexation of humus (HS) with HMs but had less effect on Ni. In addition, the optimum concentration of wood vinegar (WV) was determined to be 1.75%. The results of the study showed that in the Pb passivation treatment group, the proportion of soluble (Red) and exchangeable states (Exc) converted to oxidized (Oxi) and residual states (Res) was 8%, 14%, 6%, 1%, and 12% in the CK, T1, T2, T3, and T4 treatment groups, respectively; in the Cr passivation treatment group, the proportion of Cr-Red and Cr-Exc converted to oxidized and residual states was 31%, 33%, 25%, 29%, and 25%; in the Cd passivation treatment group, the proportions of Cd-Red and Cd-Exc converted to oxidized and residual states were 5%, 15%, 4%, 9%, and 11%, respectively; whereas the Ni treatment group did not show any significant passivation effect. The proportion of Pb-Oxi was relatively stable, Cr-Oxi was converted to Cr-Res, whereas Cd showed the conversion of Cd-Oxi to Cd-Exc. SUVA254 and SUVA280 showed significant positive correlations with Pb-Res, Cr-Res and Ni-Res, and significant positive correlations with moisture content (MC); whereas MC was significantly negatively correlated with each form of HMs. Total potassium (TK), total nitrogen (TN), and both carbon (TOC) were negatively correlated with Pb-Res and Pb-Exc. Structural equation modeling verified the relationship between environmental factors and HMs, and the composting results showed that the addition of biochar (BC) and a higher percentage of WV could increase compost decomposition and passivate HMs to improve its agronomic function.

The effect of calcium hydroxide addition on enhancing ammonia recovery during thermophilic composting in a self-heated pilot-scale reactor

A modified outdoor large-scale nutrient recycling system was developed to compost organic sludge and aimed to recover clean nitrogen for the cultivation of high-value-added microalgae. This study investigated the effect of calcium hydroxide addition on enhancing NH₃ recovery in a pilot-scale reactor self-heated by metabolic heat of microorganisms during thermophilic composting of dewatered cow dung. 350 kg-ww of compost was prepared at the ratio of 5: 14: 1 (dewatered cowdung: rice husk: compost-seed) in a 4 m³ cylindrical rotary drum composting reactor for 14 days of aerated composting. High compost temperature up to 67 °C was observed from day 1 of composting, proving that thermophilic composting was achieved through the self-heating process. The temperature of compost increases as microbial activity increases and temperature decreases as organic matter decreases. The high CO₂ evolution rate on day 0-2 (0.02-0.08 mol/min) indicated that microorganisms are most active in degrading organic matter. The increasing conversion of carbon demonstrated that organic carbon was degraded by microbial activity and emitted as CO₂. The nitrogen mass balance revealed that adding calcium hydroxide to the compost and increasing the aeration rate on day 3 volatilized 9.83 % of the remaining ammonium ions in the compost, thereby improving the ammonia recovery. Moreover, Geobacillus was found to be the most dominant bacteria under elevated temperature that functions in the hydrolysis of non-dissolved nitrogen for better NH₃ recovery. The presented results show that by thermophilic composting 1 ton-ds of dewatered cowdung for NH₃ recovery, up to 11.54 kg-ds of microalgae can be produced.

The role of probiotics in vannamei shrimp aquaculture performance – A review

Vannamei shrimp (Litopenaeus vannamei) is an important food commodity of economic benefit due to its high price, low susceptibility to disease, and popularity for consumption. These advantages have led many farmers to cultivate vannamei shrimp. Efforts are underway to improve the aquaculture performance of this species, including the use of probiotics, which are non-pathogenic bacteria that aid in digestion and help fight disease. Probiotics are usually obtained from the intestines of vannamei shrimp or the culture environment. They are low-cost, non-pathogenic, and largely non-toxic source of antibiotics and are able to synthesize various metabolites that have antibacterial functions and applications. Research on probiotic use has primarily been focused on increasing vannamei shrimp aquaculture production. Bacterial species, such as Lactobacillus or Nitrobacter, can be administered orally, by injection, or as a supplement in aquaculture water. Probiotics help to improve survival rate, water quality, immunity, and disease resistance through space competition with disease-causing bacteria, such as Vibrio spp. An increased number of probiotic bacteria suppresses the growth and presence of pathogenic bacteria, which lowers disease susceptibility. In addition, probiotic bacteria also aid digestion by breaking down complex compounds into simpler substances that the body can absorb more easily. This mechanism improves growth performance in terms of weight, length, and feed conversion ratio. This review aimed to provide information regarding contribution of probiotic to improve vannamei shrimp production in aquaculture. Keywords: application, bacteria, farm, microbiome, shrimp.

Impacts of composting duration on physicochemical properties and microbial communities during short-term composting for the substrate for oyster mushrooms

A short-term composting process to prepare substrate is an effective way to cultivate oyster mushrooms (Pleurotus spp.), which can increase the yield of mushrooms and lower the rate of contamination in non-industrialized cultivation. Moreover, it is different from the traditional composting processes for fertilizers and lacks systematic study, such as microbial succession and compost quality. In this study, a series of different tests of composting duration (0, 2, 4 and 5 d) were performed. A composting duration of 4-5 d over 58 °C was suitable for mushroom cultivation based on the biological efficiency (BE) range of 69.76-73.41 % and the contamination rate of 0 %. The content of total carbon (TC) continuously decreased during composting, while the content of total nitrogen (TN) reacted in an opposite matter. The final TN and C/N ratios were 1.89 % and 28/1, respectively, which fell well within the optimal range of nutritional requirements for oyster mushroom cultivation. The composting bacteria were more diverse than the fungal species. Caldibacillus, Thermobispora, Thermopolyspora, Thermobacillus and Ureibacillus were the predominant bacterial genera during the thermophilic stage. Co-occurrence patterns of microbial communities and physicochemical properties were performed using a network analysis, which indicated that bacteria can play more efficient roles than fungi in the degradation of organic matter. The structural equation model showed that composting duration significantly affected bacterial diversity, lignocellulose degradation rates, and BE. The correlations between bioinformatics parameters with composting characters and agronomic traits were determined by the Mantel test and showed that the induction of bacterial diversity over time rapidly activated carbon metabolism during short-term composting. This study provides a new idea of agro-waste composting for mushroom cultivation.