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Lignocellulosic biomass is the most abundant source of organic materials available, yet it remains highly underutilized as a source of renewable energy products. The complex and rigid properties of lignocellulosic materials make the biomass difficult to digest, and thus it does not offer a significant energy yield once digested through anaerobic digestion (AD). Several pretreatment methods have been developed over the past years to improve the digestibility of lignocellulosic biomass and enhance its energy yield potential. This Review examines the latest technologies and methods used in the pretreatment of lignocellulosic biomass for more efficient AD and energy yield in the form of methane gas. Such pretreatment processes include mechanical, irradiation, thermal, chemical, biological, and combined pretreatment. A comparison between the different types of available pretreatment methods shows that the different methods have been successful in achieving an improvement in the methane yield from lignocellulosic substrates on a laboratory scale. There is a clear variation in the energy requirements, reaction times, and methane improvement for each method. However, more research is necessary to assess the applicability and feasibility of such methods on full-scale facilities. In addition, the optimum choice of a pretreatment process will remain highly dependent on the substrate type and economic feasibility.

Growth performance, mortality and carotenoid pigmentation were studied in triplicate groups each with 1000 swim-up larvae of rainbow trout (Oncorhynchus mykiss), derived from five groups of female broodstock fed diets with 0.07, 12.5, 33.3, 65.1 or 92.9 mg astaxanthin kg )1 , respectively. The first feeding fry (initial weight range from 113 to 148 mg) were fed a diet not supplemented with carotenoids in an experiment lasting 45 days. Fry were initially sampled for astaxanthin content and initial weight, and in subsequent 15-day intervals to determine weights, condition factors (CF), specific growth rates (SGR) and thermal growth coefficients (TGC). Total carotenoid concentration of the larvae was highly linearly correlated to that of the eggs (r 2 = 0.97, P = 0.002). About 59-67% of fry carotenoids consisted of esterified astaxanthin, and on average 39.7% of the egg carotenoids were recovered in the fry. Overall (0-45 days) SGRs and TGCs were significantly higher (P < 0.05) in the offspring of the four groups of females fed supplemented diets (12.5-92.9 mg astaxanthin kg )1 ) than in offspring of females fed the non-supplemented diet. TGCs (0-45 days) within groups derived from broodstock supplemented with astaxanthin were similar (P > 0.05), but higher than in the group derived from females fed the diet not supplemented with astaxanthin (P < 0.05). Mortality (average 0.76%) was not significantly affected by treatment. The study indicates that dietary supplement of astaxanthin (>12.5 mg kg )1 ) to maternal broodstock diets improves offspring SGR and TGC with up to 33 and 38%, respectively.

Low frequency ultrasound (LFUS) was evaluated as a novel disinfection technique within recirculating aquaculture systems both individually and combined with UV-C. Dose-dependent inactivation rates were determined for the total viable counts and model organisms representing different taxa of common fish parasites: the ciliate Paramecium sp., second larval stage (L2) of the nematode Anguillicola crassus and metanauplii of Artemia sp. Application of LFUS up to 19 kJ/L did not reduce the number of colony forming units (CFU), whilst UV-C irradiation was highly effective. Pre-treatment with LFUS reduced the mean size of suspended solids in aquaculture water and thus increased the germicidal effect of UV-C by up to 0.6 log units. LFUS was effective against the eukaryotic organisms, and the dose-dependent inactivation could be well described by functions of an exponential decay. However, the efficiency of LFUS differed greatly between species. A LFUS dose of 1.9 kJ/L (consumed energy) was sufficient to inactivate Artemia by 99%, but a ten times higher dose was necessary to inactivate 95% and 81% of Paramecium and Anguillicola larvae, respectively. In clear water, the energetic efficiency of UV-C (emitted by a low pressure lamp) against Paramecium and Anguillicola larvae was higher compared to LFUS, but LFUS was more efficient against Artemia. However, the efficiency of LFUS against ciliates or nematode larvae would be similar or even higher than UV-C in highly turbid water or if less efficient medium pressure lamps are used. This study shows that LFUS can be applied safely at energy densities that are effective against a wide range of parasites like ciliates, nematodes and crustaceans. The combination of LFUS and UV-C could provide an appropriate water treatment with regards to all relevant pathogens in recirculating aquaculture systems.

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