Mitsuhiko Koyama

Nagasaki University

Aquatic weeds including submerged macrophyte have been excessively propagated and causing environ-mental issues in freshwater environment of many countries, and the sustainable treatments have been investigated. In the present study, five submerged macrophyte species dominant in Lake Biwa, Japan, Cer-atophyllum demersum, Egeria densa, Elodea nuttal...

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 d...

This study aimed to elucidate the recovery of organic matter decomposition after oxygen deficiency in the early stage was replaced by aerobic conditions during composting. Oxygen deficiency at the early stage was created by supplying nitrogen gas into the composting for 3 days (LN3dA) and 5 days (LN5dA). Subsequently, air was introduced until the e...

The use of an enriched microbial community as an inoculum during composting is expected to be effective in accelerating the decomposition of organic matter. In this study, to enhance the efficiency of organic matter decomposition, the effect of storage time on an enriched microbial community was evaluated using a temperature-controlled lab-scale re...

The blooming of the world’s human population and the transition of the human diet into a more westernized, high-protein diet has accelerated the production of slaughterhouse wastewater (SWW) as the number of meat processing plants (MPP) has increased in the past few decades. Conventional treatment processes (CTP) used in treating SWW, such as anaer...

The study aimed to elucidate the effect of oxygen supply rate (OSR) on the composting of model organic waste independently from other factors by using a controlled laboratory-scale reactor system. Four OSRs, 96.2, 24.2, 13.7, and 3.45 mL-O2/min/kg-WS (wet solid), were tested. The delay of organic matter degradation was observed temporarily in the e...

This study elucidated the changes in the short-term response to organic load shocks of the anaerobic digestion (AD) microbiome acclimatized to a simple substrate and a complex substrate. Batch vial reactors were inoculated with AD sludge acclimatized to either a simple (starch and hipolypeptone) or a complex (dog food and starch) substrate, both wi...

Fluctuations in the anaerobic digestion (AD) organic loading rate (OLR) cause shocks to the AD microbiome, which lead to unstable methane productivity. Managing these fluctuations requires a larger digester, which is impractical for community-scale applications, limiting the potential of AD in advancing a circular economy. To allow operation of sma...

Anaerobic digestion treatment of excessively growing aquatic weeds has been paid attention due to the energy recovery with low energy requirement. The effects of lignocellulosic components on anaerobic digestibility of terrestrial herbaceous plants have been extensively researched, not much work has been done on aquatic weeds. Because of the flexib...

For the composting aeration, positive aeration (PA, blow type) is commonly used but suffers from the problem of odor diffusion, while negative aeration (NA, suction type) is scarcely used but it can minimize odor. However, the effect of aeration type on the organic matter degradation rate in large-scale composting is still unknown. In this study, w...

Hydrothermal treatment (HTT) as a pretreatment method for compost raw material has multiple benefits such as enhanced solubility of organic material, improved bioaugmentation, and reduced biohazard by killing harmful microorganisms. In this study, we pretreated food waste via HTT at 180 °C for 30 min to investigate its effect on food waste composti...

Fluctuations in organic loading rate are frequently experienced in practical-scale anaerobic digestion systems. These impose shocks to the microbiome leading to process instability and failure. This study elucidated the short-term changes in biochemical pathways and the contributions of microbial groups involved in anaerobic digestion with varying...

The positive effect of seeding inoculation on the enhancement of organic matter decomposition has been reported only for specific substrates (lignocellulose and organic acids). However, in most cases (food waste or sludge), no effect has been reported. This study aimed to clarify the effect of seeding materials by quantitatively analyzing the relat...

In recent years, attempts have been made to develop a thermophilic composting process for organic sludge to produce ammonia gas for high value-added algal production. However, the hydrolysis of non-dissolved organic nitrogen in sludge is a bottleneck for ammonia conversion. The aim of this study was to identify enzymes that enhance sludge hydrolysi...

Anaerobic digestion is a mature technology; however, the mechanism of cell proliferation during starvation has not yet been clarified. In this study, a continuous stirred tank reactor (CSTR) treating food waste was exposed to deliberate starvation for 12 days. The cell density and the variability of digestate characteristics during starvation were...

Recent attempts have been made to develop a thermophilic composting process for organic sludge to not only produce organic fertilizers and soil conditioners, but to also utilize the generated ammonia gas to produce high value-added algae. The hydrolysis of organic nitrogen in sludge is a bottleneck in ammonia conversion, and its improvement is a ma...

Microalgae can use either ammonium or nitrate for its growth and vitality. However, at a certain level of concentration, ammonium nitrogen exhibits toxicity which consequently can inhibit microalgae productivity. Therefore, this study is aimed to investigate the tolerance of Tetraselmis tetrathele to high ammonium nitrogen concentrations and its ef...

Anaerobic digestion is an effective method for treating excessive submerged macrophytes, which are causing severe environmental issues worldwide. The biomethane potential (BMP) of submerged macrophytes varies depending on the seasonal changes in the lignin content of each species and the species composition of harvested submerged macrophytes. In th...

Aquatic plant biomass is characterised by a high moisture content and a lignocellulose structure. To apply the anaerobic digestion (AD) treatment to aquatic plants, with simultaneous achievement of high methane (CH4) recovery per biomass volume and high biodegradability, has been a challenge owing to these characteristics. Herein, we propose a nove...

Continuous cultivations of the microalga Chlorella sorokiniana using 10-L flat-panel bioreactors were conducted at different pH levels and hydraulic retention times (HRT) under natural light conditions to accomplish the maximum algal yields and high nutrient removal from anaerobic digestion effluent (ADE) of aquatic macro-phytes, which contained high c...

Maintaining proper aerobic conditions is a crucial factor in composting. Positive aeration (PA, blowing) has been widely applied but diffuses the odorous exhaust gas to the atmosphere. Negative aeration (NA, suction) enables to minimize the gas diffusion, but NA has scarcely been applied mainly because there has been no clear answer about the advan...

Maximizing the recovery of gaseous NH 3 during thermophilic composting of shrimp pond sludges is an attractive approach to produce clean nitrogen used for the cultivation of high-value microalgae. This study investigated the NH 3 recovery potential and the related microbial community changes during thermophilic composting of shrimp pond sludges. Th...

Lactic acid bacteria are observed during early stages of almost all food waste composting. Among them, 2 types of lactic acid bacteria, Pediococcus (homofermentative lactic acid bacterium) and Weissella (heterofermentative lactic acid bacterium) have been often reported. In this study, the roles of these 2 types of lactic acid bacteria in the compo...

Changes in the microbial community were investigated during the acclimation process of anaerobic digestion while treating synthetic lipid-rich wastewater, which comprised of glucose, acetic acid, lactic acid, and soybean oil. The oil content in the synthetic wastewater was increased successively from 0% to 25% and finally to 50% of the total carbon...

This study attempted to characterize the microbial community and its role in anaerobic digestion of lipid. Reactors were fed semi-continuously with three related substrates, oil and its degradation intermediates (glycerol and long chain fatty acids (LCFAs)), with a stepwise increase in organic loading rate for 90 days. Microbial community analysis...

The primary biological treatment method for organic sludge is composting and/or anaerobic digestion, but their product (compost or biogas) is of little economic benefit; therefore, an improved process to produce a high-value product is required to make sludge management more sustainable. Maximizing NH3 gas recovery during composting processes has t...

Composting is an advantageous method for recycling organic waste and produces organic fertilizer. Composting involves many types of microorganisms that construct complex microbial ecosystems. No previous research has attempted to determine which microorganisms commonly appear in successful (i.e. well-stabilized) composting. To produce well-stabiliz...

The present study assessed the efficiency of utilizing mixed culture bacteria (MCB) incorporated with individual nanoparticles (NPs), i.e., hematite (α-Fe2O3), nickel oxide (NiO), and zinc oxide (ZnO), dual NPs (α-Fe2O3 + NiO, α-Fe2O3 + ZnO, and NiO + ZnO), and multi-NPs (α-Fe2O3 + NiO + ZnO) for hydrogen production (HP) from industrial wastewater...

Methods for obtaining high-concentration (ca. 40 g/L) ethanol from cassava stem (CS) were explored by investigating the effects of acid hydrolysis conditions, hydrolysate concentration, and intermittent inoculation of yeast on ethanol fermentation. Two-step acid hydrolysis demonstrated that a reduction in autoclaving temperature from 121 °C to 111...

Green microalgae have great potential for removing inorganic nutrients from wastewater and anaerobic digestion effluent (ADE). We investigated the cultivation conditions for maximum algal yield and nutrient (ammonium and phosphate) removal rates. The green microalga, Chlorella sorokiniana, was cultured using ADE from anaerobic digestion by two domi...

Aim: In order to evaluate the effects of ammonia on microalgae growth, Chlorella vulgaris was cultivated in ammonium nitrogen. Methodology: The marine microalgae, Chlorella vulgaris was cultivated in algal media containing increasing concentrations of ammonium concentrations at 320, 640, 960, 1600 mg l⁻¹, with free ammonia concentrations of 0.64 to...

Aim: In this study, ethylene glycol was supplied to an algal-bacterial consortium to investigate the effect of bacterial mineralization of ethylene glycol on algal growth. Methodology: Batch cultures of bacteria and Chlorella fusca monocultures, as well as algal-bacterial consortium were fed with 14,000 mg l⁻¹ of ethylene glycol and incubated in on...

There are many problems related to overgrowth of aquatic macrophytes in many lakes and rivers throughout the world; for instance, the harvesting costs in Lake Biwa have been increasing by 200 million Japanese yen a year (equivalent to 1.8 million USD). Historically, aquatic macrophytes were harvested for use as fertilizer in agriculture in Japan, b...

Development of thermophilic composting for maximizing NH3 gas recovery would enable the production of a nitrogen source which is free from pathogen/heavy metal, for the cultivation of high-value microalgae. The present study examined the effect of NH3 recovery, nitrogen mass balance, and microbial community dynamics on thermophilic composting of sh...

Alkaline pretreatment for lignocellulosic biomass is beneficial for enhancing the anaerobic digestibility, but the rise of pretreatment cost and the dilution of substrate by the addition of a neutralizing agent and an alkaline solution are significant drawbacks. To solve these problems, utilization of acidified food waste as a co-substrate during a...

The long-term effect of alkaline pretreatment on semi-continuous anaerobic digestion (AD) of the lignin-rich submerged macrophyte Potamogeton maackianus was investigated using mesophilic and thermophilic conditions. In pretreated reactors, dissolved lignin accumulated to high levels. CH4 production under the pretreated condition was higher than tha...

To develop an effective treatment for the globally invasive Brazilian waterweed Egeria densa, anaerobic digestion was observed at 37 °C, 55 °C, and 65 °C. The average methane production rate at 55 °C was 220 mL L⁻¹ day⁻¹, which was two-fold that at 37 °C and 65 °C. Volatile fatty acid accumulation was detected under thermophilic conditions; however...

Delignification by chemical pre-treatment improves the anaerobic digestibility of lignocellulosic biomass, but the by-products can potentially inhibit the digestion process. The present study investigates the inhibitory effect of dissolved lignin on three steps of anaerobic digestion: methanogenesis, acidogenesis, and hydrolysis. Dissolved lignin w...

The present study investigated the effect of alkaline thermochemical pre-treatment on anaerobic digestibility of two submerged macrophyte species which have significantly different lignin content. The highest hydrolysis efficiency was achieved at NaOH loading rate of 0.20 g g-TSsubstrate−1, 80 °C, 3.0 h for both species. Alkaline delignification wa...