Reduction of sludge production from WWTP using thermal pretreatment and enhanced anaerobic methanisation.

The objective of the study presented here was to investigate the performance of an enhanced two-step anaerobic process for the treatment of WWTP sludge. This process was developed to answer the urgent need currently faced by WWTP operators to reduce the production of biosolids, for which disposal pathways are facing increasing difficulties. A pilot plant was operated on a full-scale WWTP (2,500 p.e.) over a period of 4 months. It consisted of a thermal pre-treatment of excess sludge at 175 degrees C and 40 min, followed by dewatering and methanisation of the centrate in a fixed-film reactor. The thermal lysis had a two-fold enhancing effect on sludge reduction efficiency: firstly, it allowed a decrease of the HRT in the methaniser to 2.9 days and secondly, it yielded biosolids with a high dewaterability. This contributed to further reductions in the final volume of sludge to be disposed of. The two-step process achieved a sludge reduction efficiency of 65% as TSS, thus giving an interesting treatment option for WWTP facing sludge disposal problems.     

Acceleration waves through a mixture of two non-linear elastic solids

Summary In this paper we study the propagation of acceleration waves through an anisotropic isothermal mixture of two non-linear elastic solids. First of all, we show that, under suitable hypotheses on the constitutive equations, there exist twelve real normal speeds of propagation; then by means of Nariboli method, we state the evolution law of the discontinuities along the rays associated with the wave front.Work performed under the auspices of C.N.R. (GNFM) and supported by M.P.I. of Italy.     

Uniqueness and reciprocity in the boundary-initial value problem for a mixture of two elastic solids occupying an unbounded domain

Summary In this paper two uniqueness theorems for an anisotropic mixture of two linear elastic solids are established: The former concerns the mixed boundary-value problem, the latter the displacement problem. These theorems are proved for unbounded domains in the absence of artificial restrictions upon the behaviour of the unknown fields at infinity. A reciprocity theorem is also given.     

Techno-Economic Evaluation of Biodiesel Production from Waste Cooking Oil—A Case Study of Hong Kong

Fossil fuel shortage is a major challenge worldwide. Therefore, research is currently underway to investigate potential renewable energy sources. Biodiesel is one of the major renewable energy sources that can be obtained from oils and fats by transesterification. However, biodiesel obtained from vegetable oils as feedstock is expensive. Thus, an alternative and inexpensive feedstock such as waste cooking oil (WCO) can be used as feedstock for biodiesel production. In this project, techno-economic analyses were performed on the biodiesel production in Hong Kong using WCO as a feedstock. Three different catalysts such as acid, base, and lipase were evaluated for the biodiesel production from WCO. These economic analyses were then compared to determine the most cost-effective method for the biodiesel production. The internal rate of return (IRR) sensitivity analyses on the WCO price and biodiesel price variation are performed. Acid was found to be the most cost-effective catalyst for the biodiesel production; whereas, lipase was the most expensive catalyst for biodiesel production. In the IRR sensitivity analyses, the acid catalyst can also acquire acceptable IRR despite the variation of the WCO and biodiesel prices.     

Simulation and Prediction of Methyl‐mercaptan Removal by Chemical Scrubbing with Hydrogen Peroxide

A model has been developed in order to predict the behavior of methylmercaptan chemical scrubbing using hydrogen peroxide. New constants concerning reactions involving methylmercaptan have been proposed based on mass transfer and kinetic equations for the dissociation of methylmercaptan by the hydroxide and the reaction with perhydroxyl ions. Once this step has been achieved, the model is used to characterize the influences of the different chemical scrubbing operating parameters, i.e., the gas‐liquid contact time, the oxidant concentration, and the pH. As expected, an increase in the hydrogen peroxide concentration, the contact time, or the pH leads to an increase in the methylmercaptan removal level. However, the most interesting aspect of the model lies in the possibility of defining a new or limiting value for each parameter, below which the process is not efficient enough to be industrially implemented.     

Starmerella bombicola: recent advances on sophorolipid production and prospects of waste stream utilization

Sophorolipids are among the most extensively studied microbial biosurfactants. Starmerella bombicola is the most productive strain known for sophorolipid production, with volumetric productivity of up to 3.7 g L⁻¹ h⁻¹. This review focuses on the two most important aspects that have an influence on sophorolipid commercialization. Firstly, the metabolic engineering achievements of S. bombicola in the last decade are summarized. Secondly, three improvements of the bioprocess are described, including alternative feedstock, fermentation strategy and specially designed bioreactor. Discussion is made on the waste sources that have been used as feedstock for sophorolipid production, and the review also emphasizes the potential of food waste as nutrient source. Fermentation strategies that correlate with the specially designed bioreactors for commercialization are also discussed in detail. © 2018 Society of Chemical Industry     

Ammonia removal from effluent streams of wet oxidation under high pressure

The formation of ammonia is inevitable during industrial-scale wet oxidation of wastewater if nitrogen-containing compounds are present. This undesired side-reaction requires additional measures for disposal. Common routes are either the use of noble metal-containing catalysts in the first oxidation step or end-of-pipe treatment. Problems rise for example from the insufficient stability of solid catalysts against hydrothermal impact. As most of the wet oxidation processes run at elevated pressure and temperature, running the heterogeneously catalysed oxidation of ammonia in the gas phase in a downstream reactor could protect the catalysts mainly from leaching and offers an economic alternative by avoiding loss of unused oxygen after depressurisation. This work reports on the oxidation of ammonia with air in steam atmosphere using Cu,Cr-containing supported and bulk catalysts at 235–305 °C and 30–60 bar. A copper chromite catalyst gave best performance (86% conversion at 305 °C, 45 bar, contact time 1 s). The spinel-type phase CuCr₂O₄ seems to be the active phase and shows superior stability. The results indicate that phase behaviour of water strongly influences activity and lifetime of catalysts. Characterisation of the solids (BET, XRD, XPS, ICP) proved that deactivation is mainly caused by leaching of Cr(VI) species from catalysts when the reaction runs near to dew point of water and by loss of BET surface area of supported catalysts due to hydrothermal impact.A member of the EU-funded Coordination Action of Nanostructured Catalytic Oxide Research and Development in Europe (CONCORDE).     

Minimisation of excess sludge production in a WWTP by coupling thermal hydrolysis and rapid anaerobic digestion.

In many cases, reducing sludge production could be the solution for wastewater treatment plants (WWTP) that here difficulty evacuating the residuals of wastewater treatment. The aim of this study was to test the possibility of minimising the excess sludge production by coupling a thermal hydrolysis stage and an anaerobic digestion with a very short HRT. The tests were carried out on a 2,500 p.e. pilot plant installed on a recycling loop between the clarifier and the actived sludge basin. The line equipped with the full scale pilot plant produced 38% TSS less than the control line during a 10 week period. Moreover, the rapid anaerobic digestion removed, on average, more than 50% of the total COD load with a hydraulic retention time (HRT) of 3 days. Lastly, the dryness of the remaining excess sludge, sanitised by the thermal hydrolysis, was more than 35% with an industrial centrifuge. This combination of thermal hydrolysis and rapid anaerobic digestion equally permits a significant gain of compactness compared to traditional anaerobic digesters.     

Use of hydrogen peroxide in scrubbing towers for odor removal in wastewater treatment plants.

The aim of this work was to replace sodium hypochlorite (NaCIO) with hydrogen peroxide (H202) in chemical scrubbing towers, in order to avoid the formation of chlorinated species, harmful for human health. Some previous studies have already shown the ability of H2O2 to treat the hydrogen sulfide (H2S) pollution. However, an important decomposition of the oxidant was observed in the scrubbing solution (carbonates, transition metal and high pH are responsible for this decomposition) leading to high reactant consumption. Consequently, this study first focused on research into a compound able to reduce the hydrogen peroxide degradation. Experiments were conducted on a pilot unit (3,000 m3 h(-1)) in a wastewater treatment plant. The sodium silicate (Na2SiO3) proved to be a good scrubbing solution stabilizer. A very good removal of hydrogen sulfide (up to 98%) was also obtained. Finally, the study resulted in the determination of the best operating conditions to achieve both an efficient and economical process.