Microfiltration and ultrafiltration as a post-treatment of biogas plant digestates for producing concentrated fertilizers

Abstract

Biogas plant digestate liquid fractions from biogas plants can be concentrated by microfiltration and ultrafiltration. Two types of microfiltration membranes (polysulphone (PS) and surface modified polyvinylidene fluoride (PVDF)) were used to process digestate liquid fractions, and to assess their applicability in the recovery of particulate phosphorus compared to an ultrafiltration membrane (polyethersulphone (PES)). Results show that membrane material, operational conditions and pore diameter influenced the permeate flux pattern during microfiltration. The PS membranes initially had a higher tendency to foul than PVDF membranes. However, during the filtration process, as fouling built up, the permeate flux behaviour of the two membranes became very similar. During the concentration of digestate liquid fractions, the microfiltration PS membrane and the ultrafiltration 19 PES membrane achieved the highest phosphorus rejection (80 % w/w.), suggesting that there was a 20 correlation between the membrane material and both the fouling trend and phosphorus rejection. A 21 two-step basic-acidic cleaning was unable to recover the initial water flux for the fouled 22 microfiltration membranes. In conclusion, the PS microfiltration membranes might be a good 23 strategy for recovering phosphorus from digestate liquid fractions. Further research leading to 24 2 adequate cleaning procedures for microfiltration PS and PVDF membranes treating digestate liquid fractions though are needed.

Liquid fertilizer products from anaerobic digestion of food waste: mass, nutrient and energy balance of four digestate liquid treatment systems

“…Anaerobic digestion (AD) of food waste (FW) is increasingly used to produce renewable energy, in the form of heat and power or vehicle fuel, and nutrient-rich digestate for agriculture, to decrease the use of energy intensive mineral fertilizers . However, the digestate has usually unbalanced nutrient ratios for plant growth (Camilleri-Rumbau et al, 2014). Large mass due to high water content increases the transportation need of the digestate, as the AD plants treating municipal FW are usually located far from agricultural lands (Babson et al, 2013).…”

Application of aquaporin-based forward osmosis membranes for processing of digestate liquid fractions

“…Previous studies on digestates LFs have described that particles mean and median sizes vary from 31 to 257 µm and from 14 to 116 µm, respectively [31]. Based on this, it is reasonable to select a sieve mesh size of 2mm, 350 µm and 125µm to remove the coarse solids present in the studied LFs to mitigate potential membrane surface damages or excessive fouling [32]. Pre-meshing reduced total solids of the LF from 49 g L -1 to 36 g L -1 after meshing with 350-125 µm sieving.…”

Prognostic Assessment of the Viability of Hydrothermal Liquefaction as a Post-Resource Recovery Step after Enhanced Biomethane Generation Using Co-Digestion Technologies

“…In Equations 14- (19), w represents the fractional moisture content of the digestate feedstock, T represents the HTL reaction temperature, in K, B m is the measured experimental biomethane potential in m 3 per kg, ρ b is the density of biogas in kg/m 3 , m biogas denotes the mass of biogas in kg, x m is the volumetric fraction of biomethane in the biogas determined experimentally, m s is the mass of the substrate mixture in kg, c ps is the specific heat capacity of the substrate mixture in kJ/kg•K, ∆T denotes the temperature difference between the temperature of the feed substrate (ambient temperature, 298.15 K) and the target substrate temperature (mesophilic temperature, 310.15 K) and the constant number 1.3 is the factor used to account for the heat losses from the digester. According to previous studies, the specific heat capacity of the digestate mixture can be assumed to be constant and is approximately equal to the specific heat capacity of water of 4.184 KJ/kg•K [61][62][63].…”

“…A simplified illustration of the proposed one-step digestate processing technology compared to existing digestate processing technologies is presented in Figure 1. Figure 1 shows that digestate handling requires a solid-liquid phase separation stage to enable the separation of the solid and the liquid phases [19]. Having separated the solid and the liquid phases, a portion of the separated liquid fraction is subjected to tertiary treatment via advanced oxidation technologies to sterilize the liquid fraction prior to its disposal in surrounding water bodies [1].…”

“…Proposed enhanced resource recovery step B compared to traditional digestate handling technologies A: SY, WHDS and HTL denote stockyard, wet hydrolyzed dissolved air flotation DAF sludge and hydrothermal liquefaction, respectively; SY: stockyard; WHDS: wet hydrolyzed DAF sludge; HTL: hydrothermal liquefaction; DAF: dissolved air flotation sludge. Figure 1 shows that digestate handling requires a solid-liquid phase separation stage to enable the separation of the solid and the liquid phases [19]. Having separated the solid and the liquid phases, a portion of the separated liquid fraction is subjected to tertiary treatment via advanced oxidation technologies to sterilize the liquid fraction prior to its disposal in surrounding water bodies [1].…”