Hydrothermal conversion of toilet waste: effect of processing conditions on gas phase emissions.

Globally, many populations suffer from a lack of access to basic sanitation facilities. This is partly caused by a combination of water resource shortages and the high cost of conventional centralised treatment systems. A novel decentralised treatment technology based on sub-critical hydrothermal processing of organic wastes at toilet-scale, contributes to addressing these economic and resource limitations.

An improved model for the kinetics of non-oxidative hydrothermal process.

Hydrothermal processing as a post-treatment technology for sludge has attracted great interest globally as it could reduce the amount of sludge considerably. This experimental study developed a comprehensive kinetic model of cellulose degradation via non-oxidative hydrothermal processing at various temperatures (ranges 180-260 °C). Values of activation energies and pre-exponential factors were determined using chemical oxygen demand (COD)-based lumped concentrations.

Rheological Behavior of High Cell Density LS46 Cultures during Production of Medium Chain Length Polyhydroxyalkanoate (PHA) Polymers.

The rheology of high-cell density (HCD) cultures is an important parameter for its impact on mixing and sparging, process scale-up, and downstream unit operations in bioprocess development. In this work, time-dependent rheological properties of HCD LS46 cultures were monitored for microbial polyhydroxyalkanoate (PHA) production. As the cell density of the fed-batch cultivation increased (0 to 25 g·L cell dry mass, CDM), the apparent viscosity increased nearly nine-fold throughout the fed-batch process.

Development of High Cell Density Cultivation Strategies for Improved Medium Chain Length Polyhydroxyalkanoate Productivity Using LS46.

High cell density (HCD) fed-batch cultures are widely perceived as a requisite for high-productivity polyhydroxyalkanoate (PHA) cultivation processes. In this work, a reactive pulse feed strategy (based on real-time CO or dissolved oxygen (DO) measurements as feedback variables) was used to control an oxygen-limited fed-batch process for improved productivity of medium chain length (mcl-) PHAs synthesized by LS46. Despite the onset of oxygen limitation half-way through the process (14 h post inoculation), 28.

Hydrogen Oxidation Influences Glycogen Accumulation in a Verrucomicrobial Methanotroph.

Metabolic flexibility in aerobic methane oxidizing bacteria (methanotrophs) enhances cell growth and survival in instances where resources are variable or limiting. Examples include the production of intracellular compounds (such as glycogen or polyhydroxyalkanoates) in response to unbalanced growth conditions and the use of some energy substrates, besides methane, when available. Indeed, recent studies show that verrucomicrobial methanotrophs can grow mixotrophically through oxidation of hydrogen and methane gases respiratory membrane-bound group 1d [NiFe] hydrogenases and methane monooxygenases, respectively.

The impact of environmental parameters on the conversion of toluene to CO and extracellular polymeric substances in a differential soil biofilter.

The fraction of pollutant converted to CO versus biomass in biofiltration influences the process efficacy and the lifetime of the bed due to pressure drop increases. This work determined the relative quantitative importance and potential interactions between three critical environmental parameters: toluene concentration (Tol), matric potential (ψ) and temperature (T) on % CO, elimination capacity (EC) and the production rate of non-CO products. These parameters are the most variable in typical biofilter operation.

The role of dissolved oxygen content as a modulator of microbial polyhydroxyalkanoate synthesis.

Polyhydroxyalkanoates (PHAs) are a diverse class of bio-polymers synthesized by bacteria, usually during imbalanced growth conditions. Optimizing PHA productivity is highly dependent on the bioreactor oxygen transfer rate (OTR), which is an important consideration for process performance and economics, particularly with increasing scale. Relatively few in-depth studies are available regarding the effect of OTR and dissolved oxygen content (DOC) on PHA formation, synthesis rates, composition, and characteristics.

Carbon flux to growth or polyhydroxyalkanoate synthesis under microaerophilic conditions is affected by fatty acid chain-length in Pseudomonas putida LS46.

Economical production of medium-chain length polyhydroxyalkanoates (mcl-PHA) is dependent on efficient cultivation processes. This work describes growth and mcl-PHA synthesis characteristics of Pseudomonas putida LS46 when grown on medium-chain length fatty acids (octanoic acid) and lower-cost long-chain fatty acids (LCFAs, derived from hydrolyzed canola oil) in microaerophilic environments. Growth on octanoic acid ceased when the oxygen uptake rate was limited by the oxygen transfer rate, and mcl-PHA accumulated to 61.

Effect of hydrodynamic mixing conditions on wet oxidation reactions in a stirred vessel reactor.

The aim of this study was to investigate the impact of mixing intensity and mixing flow patterns on solid waste degradation, and production of valuable intermediate by-products such as acetic acid. Total suspended solids generally decreased, soluble chemical oxygen demand, dissolved organic carbon, and acetic acid concentration generally increased with the progress of the reaction and increase in the mixing intensity. The results showed that axial-radial flow pattern (using pitch blade impeller) and medium impeller speed (500 rpm) resulted in a higher degree of solid degradation and production of acetic acid.

Mixed culture polyhydroxyalkanoate (PHA) synthesis from nutrient rich wet oxidation liquors.

Organic waste residues can be hydrothermally treated to produce organic acid rich liquors. These hydrothermal liquors are a potential feedstock for polyhydroxyalkanoate (PHA) production. We investigated the effect of dissolved oxygen concentration and substrate feeding regimes on PHA accumulation and yield using two hydrothermal liquors derived from a mixture of primary and secondary municipal wastewater treatment sludge and food waste.

Mixotrophy drives niche expansion of verrucomicrobial methanotrophs.

Aerobic methanotrophic bacteria have evolved a specialist lifestyle dependent on consumption of methane and other short-chain carbon compounds. However, their apparent substrate specialism runs contrary to the high relative abundance of these microorganisms in dynamic environments, where the availability of methane and oxygen fluctuates. In this work, we provide in situ and ex situ evidence that verrucomicrobial methanotrophs are mixotrophs.

Fundamental mechanisms and reactions in non-catalytic subcritical hydrothermal processes: A review.

The management and disposal of solid waste is of increasing concern across the globe. Hydrothermal processing of sludge has been suggested as a promising solution to deal with the considerable amounts of sludge produced worldwide. Such a process not only degrades organic compounds and reduces waste volume, but also provides an opportunity to recover valuable substances.

Rheological measurements as a tool for monitoring the performance of high pressure and high temperature treatment of sewage sludge.

Hydrothermal processing plays a significant role in sewage sludge treatment. However, the rheological behaviour of sludge during these processes is not fully understood. A better understanding of the sludge rheology under hydrothermal processing conditions can help improve process efficiency.

Hydrothermal processing of cellulose: A comparison between oxidative and non-oxidative processes.

This study investigates oxidative and non-oxidative hydrothermal processing of cellulose at five different temperatures (180-260°C). Volatile fatty acids (VFAs) concentration, total suspended solid (TSS) degradation, dissolved organic carbon (DOC) and chemical oxygen demand (COD) were measured and compared in both processes. Moreover, the existence of hydrogen peroxide in both oxidative and non-oxidative processes was confirmed experimentally for the first time in literature.

Formation and degradation of valuable intermediate products during wet oxidation of municipal sludge.

The current study investigated the formation of organic acids and alcohols as major intermediate products of wet oxidation of municipal sludge. Municipal sludge was subjected to 60-min wet oxidation at temperatures ranging from 220 to 240°C, with 20bar oxygen partial pressure. Acetic acid was the main intermediate compound produced in this study, followed by propionic, n-butyric, iso-butyric and pentanoic acids and methanol.

A kinetic model of municipal sludge degradation during non-catalytic wet oxidation.

Wet oxidation is a successful process for the treatment of municipal sludge. In addition, the resulting effluent from wet oxidation is a useful carbon source for subsequent biological nutrient removal processes in wastewater treatment. Owing to limitations with current kinetic models, this study produced a kinetic model which predicts the concentrations of key intermediate components during wet oxidation.

Application of hydrothermal treatment to affect the fermentability of Pinus radiata pulp mill effluent sludge.

A hybrid technique incorporating a wet oxidation stage and secondary fermentation step was used to process Pinus radiata pulp mill effluent sludge. The effect of hydrothermal oxidation at high temperature and pressure on the hydrolysis of constituents of the waste stream was studied. Biochemical acidogenic potential assays were conducted to assess acid production resulting from anaerobic hydrolysis of the wet oxidised hydrolysate under acidogenic conditions.

A review of wet air oxidation and Thermal Hydrolysis technologies in sludge treatment.

With rapid world population growth and strict environmental regulations, increasingly large volumes of sludge are being produced in today's wastewater treatment plants (WWTP) with limited disposal routes. Sludge treatment has become an essential process in WWTP, representing 50% of operational costs. Sludge destruction and resource recovery technologies are therefore of great ongoing interest.

Relative influence of process variables during non-catalytic wet oxidation of municipal sludge.

Individual and interactive effects of process variables on the degradation of fermented municipal sludge were examined during wet oxidation. The process was carried out at 220-240°C using 1:1-2:1 oxygen to biomass ratio and 300-500 rpm stirring speed. Response surface methodology coupled with a faced-centred central composite design was used to evaluate the effect of these variables on total suspended solids, volatile suspended solids and total chemical oxygen demand.

Transformation and removal of wood extractives from pulp mill sludge using wet oxidation and thermal hydrolysis.

In order to remove wood extractive compounds from pulp mill sludge and thereby enhancing anaerobic digestibility, samples were subjected to either oxidative hydrothermal treatment (wet oxidation) or non-oxidative hydrothermal treatment (thermal hydrolysis). Treatments were carried out at 220 °C with initial pressure of 20 bar. More than 90% destruction of extractive compounds was observed after 20 min of wet oxidation.

Rheology of a primary and secondary sewage sludge mixture: dependency on temperature and solid concentration.

The main objective of this study was to investigate the rheology of mixed primary and secondary sludge and its dependency on solid content and temperature. Results of this study showed that the temperature and solid concentration are critical parameters affecting the mixed sludge rheology. It was found that the yield stress increases with an increase in the sludge solid content and decreases with increasing temperature.

Evaluation of a two-stage hydrothermal process for enhancing acetic acid production using municipal biosolids.

A two-stage hydrothermal process aimed at improving acetic acid production using municipal biosolids was evaluated against thermal hydrolysis and conventional wet oxidation process in a 600 ml Parr batch reactor. Thermal hydrolysis was conducted at 140 °C, wet oxidation at 220 °C and the two-stage process, which acted as a series combination of thermal hydrolysis and wet oxidation, at 220 °C. Initial pressure of 1 MPa was maintained in all the three processes.

Physico-chemical properties of polyhydroxyalkanoate produced by mixed-culture nitrogen-fixing bacteria.

Ultra-high molecular weight polyhydroxyalkanoates (PHAs) with low polydispersity index (PDI = 1.3) were produced in a novel, pilot scale application of mixed cultures of nitrogen-fixing bacteria. The number average molecular weight (M (n)) of the poly(3-hydroxybutyrate) (P(3HB)) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) was determined to be 2.

Determination of external and internal mass transfer limitation in nitrifying microbial aggregates.

In this article we present a study of the effects of external and internal mass transfer limitation of oxygen in a nitrifying system. The oxygen uptake rates (OUR) were measured on both a macro-scale with a respirometric reactor using off-gas analysis (Titrimetric and Off-Gas Analysis (TOGA) sensor) and on a micro-scale with microsensors. These two methods provide independent, accurate measurements of the reaction rates and concentration profiles around and in the granules.