Abstract
The development of intensive aquaculture is facing the challenge of the sustainable management of effluents. The reproductive sectors (i.e., hatcheries) mainly use water recirculation systems (RAS), which discharge a portion of wastewater. Anaerobic digestion (AD) could reduce the environmental impact of this waste stream while producing biogas. The study is focused on the biochemical methane potential (BMP) of brackish fish hatchery sludges. Wastewater was concentrated by microfiltration and sedimentation and thickened sludges were treated in a BMP system with different inoculum/substrate (I/S) volatile solids ratios (from 50:1 to no inoculum). The highest I/S ratio showed the highest BMP (564.2 NmL CH4/g VS), while different I/S ratios showed a decreasing trend (319.4 and 127.7 NmL CH4/g VS, for I/S = 30 and I/S = 3). In absence of inoculum BMP resulted of 62.2 NmL CH4/g VS. The kinetic analysis (modified Gompertz model) showed a good correlation with the experimental data, but with a long lag-phase duration (from 14.0 to 5.5 days) in particular with the highest I/S. AD applied to brackish water sludges can be a promising treatment with interesting methane productions. For a continuous, full-scale application further investigation on biomass adaptation to salinity and on retention times is needed. Further experimental tests are ongoing.
Highlights
IntroductionThe most recent data revealed that marine aquaculture systems allowed to obtain a production of 28.7 million tons, representing approximately 36% of the total production of aquaculture [1]
During the last 40 years, aquaculture grew faster than other food production sectors.The most recent data revealed that marine aquaculture systems allowed to obtain a production of 28.7 million tons, representing approximately 36% of the total production of aquaculture [1]
The total solids were determined by complete drying of the samples in a ventilated oven at 105 ◦ C for 24 h; the volatile solids were determined as the difference between the calculated Total solids (TS) and the residual ashes, where the ashes were determined after incineration of the TS sample at 600 ◦ C for about 8 h, until a constant weight was reached
Summary
The most recent data revealed that marine aquaculture systems allowed to obtain a production of 28.7 million tons, representing approximately 36% of the total production of aquaculture [1]. Production of fed finfish in marine or coastal aquaculture systems 6.6 million tons in 2016) [1] is mostly carried out with floating or submersible cages, that raise serious problems related to the produced environmental impacts from many points of view. Sea water and sediment pollution, as a matter of fact, are the most serious and difficult to control of these environmental issues, mainly due to the practical impossibility of collecting the released effluents from these sea systems [2]. The production of the fry that successively are bred in cages, instead, is normally carried out in land based brackish and marine water systems, generally with tanks located in a protect environment.
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