Fernando Fernández-Polanco

Hydrothermal multivariable approach: Full-scale feasibility study

A process configuration combining thermal hydrolysis (TH) and anaerobic digestion (AD) of sludge has been studied with the objective of analysing the feasibility of the technology for full scale installations. The study has been performed through pilot scale experiments and energy integration considerations, and a scheme of the most profitable option is presented: thermal hydrolysis unit fed with 7% total solids (TS) secondary sludge, anaerobic digestion of the hydrolysed sludge together with fresh primary sludge, and a cogeneration unit to produce green electricity and provide hot steam for the thermal hydrolysis process. From a technical and practical point of view, the process scheme proposed is considered to be feasible. Based on the results of the pilot plant performance and the laboratory studies, the process has proven to operate successfully at a concentration of 7-8% TS. After the thermal hydrolysis, sludge viscosity becomes radically smaller, and this favours the digesters mixing and performance (40% more biogas can be obtained in nearly half the residence time compared to the conventional digestion). From an economic point of view, the key factors in the energy balance are: the recovery of heat from hot streams, and the concentration of sludge. The article presents the main energy integration schemes and defines the most profitable one: an energetically self-sufficient process, with a cogeneration unit. The scheme proposed has proven to need no additional energy input for the sludge hydrolysis, generates more that 1 MW green electricity (246 kW surplus with respect to the conventional process), and produces 58% less volume of Class A biowaste. The study and balances here presented set the basis for the scale-up to a demonstration plant (hydrolysis + anaerobic digestion + cogeneration unit).

Supercritical Water Oxidation of Wastewater and Sludges – Design Considerations

The SCWO process is a promising technology for the treatment of industrial wastewaters and sludges. The commercial or industrial development of this technology mainly goes through engineering considerations, such as reactor design, solids separation and equipment corrosion. In this paper, state of the art of these topics and the flow sheets and energy and mass balances for diluted wastewater and sludge treatment are presented. This plant simulation has been done using the software ASPEN PLUS and it shows that the SCWO process is an interesting alternative from the energetic point of view. The energy integration of a SCWO plant for 2 m3/h sludges with a heating value of 23000 kJ/kg can produce 420 kW as mechanical work and 2522 kg/h of process steam (0.3 MPa). For diluted wastewater the process is autothermal for feeds with an enthalpic content of 900 kJ/kg.

Behaviour of an anaerobic expanded bed reactor in non-steady state conditions

Abstract This paper presents a series of experimental data on an expanded bed anaerobic reactor operating at high organic loading rates in non-steady state conditions. The first four experiments were conducted in start-up periods after shut-downs. In the section dedicated to behaviour in the face of fluctuations, two experiments with overloading, two with decrease in temperature and one with air inflow, have been included. In all cases, the reactor demonstrated great stability with short recovery periods.