Study of the Influence of Key Process Parameters on Furfural Production.

The present work reports the influence of key process variables on the furfural formation from leached chestnut-wood chips in a pressurized reactor. Effect of temperature, pressure, type and concentration of the catalyst solution, the steam flow rate or stripping module, the moisture content of the wood particles and geometric characteristics such as size and type of the reactor, particle size and bed height were considered systematically. One stage process was only taken into consideration. Lab-scale and pilot-scale studies were performed. The results of the non-catalysed laboratory experiments were compared with an actual non-catalysed (auto-catalysed) industrial process and with experiments on the pilot scale, the latter with 28% higher furfural yield compared to the others. Application of sulphuric acid as catalyst, in an amount of 0.03-0.05 g (H2SO4 100%)/g d.m. (dry material), enables a higher production of furfural at lower temperature and pressure of steam in a shorter reaction time. Pilot scale catalysed experiments have revealed very good performance for furfural formation under less severe operating conditions, with a maximum furfural yield as much as 88% of the theoretical value.

Anaerobic digestion of brewery spent grain in a semi-continuous bioreactor: inhibition by phenolic degradation products.

In this study anaerobic digestion of selected lignocellulosic substrate, namely brewery spent grain (BSG), was studied. In order to facilitate anaerobic digestion several types of pretreatment methods were tested such as: mechanical, chemical (alkali and acid) and thermo-chemical. The anaerobic digestion experiments were carried out in a semi-continuous stirred bioreactors with the organic loading rates between 2.9 and 3.9 kgCOD m-3 d-1 (1.9 and 2.5 kgVSS m-3 d-1 respectively) and corresponding hydraulic retention times of 33-39 days. Biogas production and composition, pH, COD, TSS and VSS, short chain fatty acids and phenolic compounds were measured. A significant inhibition of biogas production occurred, depending on the type of substrate pretreatment. There are indications that p-cresol is responsible for process inhibition when its concentration in the reaction mixture exceeds critical value between 115 and 240 mg L-1. Anaerobic digestion of chemically pretreated BSG (acid and alkali) and untreated-raw BSG was inhibited between the days 56 and 63 of the experiment, followed by thermo-chemically pretreated BSG on day 112 and mechanically pretreated BSG on day 126. Analyses of the substrates showed no phenolic compounds either in raw-untreated BSG or pretreated substrates, therefore the recorded p-cresol is an intermediate degradation product, responsible for process inhibition.

Municipal waste sludge digestion in an autothermal aerobic sequencing batch reactor.

An autothermal aerobic sequencing batch process for sludge digestion and "class A" biosolids production was developed. The process was tested in laboratory and pilot scale size up to 150 PE, which can be considered a full scale size in some cases. In this process the maximum temperatures of 61.2 degrees C and 60.2 degrees C were achieved in laboratory scale in pilot scale equipment, respectively. The degradation efficiency of total chemical oxygen demand of sludge was between 50 and 70%. Similar results were achieved using pure oxygen in laboratory scale and oxygen/air mixture 1:1 by volume. The reactor scale greatly affects the achievement of thermophilic temperature. In smaller sizes the convective heat losses are the prevailing heat sink and the process is unable to produce enough heat to reach thermophilic temperature. Larger systems produce excess heat and can be installed with less intense aeration systems. The limit of air aeration system is at the size of about 500 PE.

Minimisation and utilisation of waste mineral sludge from sodium perborate production.

Various approaches to waste minimisation, waste treatment and recycling or safe disposal of the waste mineral sludge from sodium perborate production are presented and critically discussed. Some most promising actions for waste (or its harmful potential) reduction on the production level are identified. These include: a) use of better raw materials (richer boron ore), b) improvement of the ore leaching process, and c) intensification of sludge washing and dewatering. These source reduction measures have already resulted in 50% reduction of boron content in the sludge. Utilisation of the raw or treated (e.g. dried, compacted) waste sludge could be found in agriculture, civil engineering and construction material production. Agricultural use (as a lime substitute) is based on favourable content of calcium-magnesium minerals and alkali pH value of the sludge, and simultaneous absence of heavy metals. Application in civil engineering (as an aggregate) is possible after calcination, which is costly, or as a cement kiln additive. Stabilisation of sludge before disposal, when no utilisation is available, is possible by small addition of commercial binders (e.g. Portland cement) or larger amounts of pozzolanic wastes (e.g. coal fly ash).