Understanding the acidification risk of cheese whey anaerobic digestion under psychrophilic and mesophilic conditions.

Anaerobic digestion is a suitable technology to treat cheese whey (CW), a high-strength wastewater from cheesemaking. However, CW anaerobic digestion is limited by its high biodegradability, acidic pH, and lack of alkalinity. This publication evaluated the acidification risk of CW anaerobic digestion under psychrophilic and mesophilic conditions, aiming to improve digester design, operation, and decision-making when facing instability periods. To evaluate the acidification risk of CW anaerobic digestion, biochemical methane potential (BMP) tests were carried out at four different organic loads, each under psychrophilic (20 °C) and mesophilic (35 °C) conditions. Besides methane production, pH, soluble chemical oxygen demand, volatile fatty acid and alcohols were also monitored. Experimental results showed that CW can be successfully degraded under both temperature conditions, with methane yields of 389-436 mLCH4/gVS. The organic load had a greater impact on the accumulation of intermediate products than temperature, indicating that process inhibition by overloading is plausible under psychrophilic and mesophilic conditions. However, the degradation rate under mesophilic conditions was faster than under psychrophilic conditions. Experimental results also revealed a higher imbalance between fermentation and methanogenesis rate under psychrophilic conditions, which resulted in higher concentrations of intermediate products (volatile fatty acids and alcohols) and prolonged lower pHs. These results indicate that the degradation of intermediate products is less favourable under psychrophilic conditions compared to mesophilic conditions. This implies that psychrophilic digesters have a lower capacity to recover from process disturbances, increasing the risk of process underperformance or even failure under psychrophilic conditions.

Evaluation of the production and extraction of polyhydroxybutyrate from volatile fatty acids by means of mixed cultures and B. cepacia.

The global consumption of plastics generates accelerated environmental pollution in landfills and marine ecosystems. Biopolymers are the materials with the greatest potential to replace synthetic polymers in the market due to their good biodegradability, however, there are still several disadvantages, mainly related to their production cost. Considering the above, the generation of biodegradable and biocompatible bioplastics stands out as an alternative solution, some of which are made from renewable raw materials, including polyhydroxyalkanoates PHAs. Although much research has been done on bacteria with the capacity for intracellular accumulation of PHAs, among others, it is also possible to produce PHAs using mixed microbial cultures instead of a single microorganism, using natural microbial consortia that have the capacity to store high amounts of PHAs. In this contribution, three methods for the extraction and purification of PHAs produced by fermentation using volatile fatty acids as a carbon source at different concentrations were evaluated, using the pure strain Burkholderia cepacia 2G-57 and the mixed cultures of the activated sludge from the El Salitre WWTP, in order to select the best method from the point of view of environmental sustainability as this will contribute to the scalability of the process. The mixed cultures were identified by sequencing of the 16S gene. A yield of 89% was obtained from the extraction and purification of PHA using acetic acid as a solvent, which according to its properties is "greener" than chloroform. The polymer obtained was identified as polyhydroxybutylated PHB.

Cheese whey and dairy manure anaerobic co-digestion at psychrophilic conditions: Technical and environmental evaluation.

Cheese whey (CW) and dairy manure (DM) are the main residues from the dairy industry, both of which can led to significant negative environment impacts if not properly managed. However, their combined anaerobic digestion represents an opportunity to obtain bioenergy and a stabilised material as a soil improver on the farm. Biochemical potential of methane (BMP) assays were carried out at psychrophilic conditions (20 °C) to analyse the influence on biomethane production of different CW:DM mixtures (% w/w) at different of inoculum-to-substrate ratios (ISR). Based on the BMP results, a life cycle assessment (LCA) of the cheese manufacturing process was carried out considering two scenarios (i) considering the current process, where propane gas and electricity are used for cheese production (ii) the incorporation of the biogas generated in the cheese production process in the company. BMP results showed that the best mixture between CW and DM was 65:35 (weight basis) at an organic load of 0.6 gVS/L (ISR of X). The LCA showed that CW and DM anaerobic digestion allowed to reduce the cheese manufacturing carbon footprint from through the substitution of propane by the biogas produced, changing from 5.5 to 3.1 kg CO2-eq/kg cheese produced, which indicates that according to the monthly production (633.6 kg) it would stop emitting about 1519 kg CO2-eq, i.e. a saving in terms of emissions of approximately 43,6% of the total currently generated.

Simultaneous biofiltration of H2S and NH3 using compost mixtures from lignocellulosic waste and chicken manure as packing material.

Biofiltration offers an efficient and economical alternative for the elimination of offensive odors caused by hydrogen sulfide, ammonia, and volatile organic compounds. Considering that packing materials affect the performance and represent the main installation cost, the purpose of this work was to evaluate the biofiltration of H2S and NH3 comparing three composted mixtures made from chicken manure and lignocellulosic residues (pruning waste, sugarcane bagasse, and rice husk) used as packing material. A range of gas concentrations similar to those of a municipal WWTP was used in the biofiltration of a contaminated stream performed on a laboratory scale. The results indicate that at low concentrations of H2S (6-36 ppm) and NH3 (0-1 ppm), the three biofilters showed 100% removal efficiency. Now, at the maximum levels of gas concentrations of H2S (250 ppm) and NH3 (19 ppm) while the removal efficiency of H2S remained higher than 90% in all cases, the removal efficiency of NH3 remained higher than 90% only in the sugarcane bagasse biofilter. Compost mixtures with sugarcane bagasse and rice husk are highly reliable as packing material for biofiltration at high concentration of H2S. Specifically, the sugarcane bagasse mixture had the highest removal efficiency (99% H2S and 95% NH3) and the highest elimination capacity (15 g H2S/m3h and 0.6 g NH3/m3h), making it a better option for the elimination of both gases. These results represent a contribution to the construction of a low-price elimination system of offensive odors in WTTPs and other industries.