Air-side ammonia stripping coupled to anaerobic digestion indirectly impacts anaerobic microbiome.

Air-side stripping without a prior solid-liquid phase separation step is a feasible and promising process to control ammonia concentration in thermophilic digesters. During the process, part of the anaerobic biomass is exposed to high temperature, high pH and aerobic conditions. However, there are no studies assessing the effects of those harsh conditions on the microbial communities of thermophilic digesters. To fill this knowledge gap, the microbiomes of two thermophilic digesters (55°C), fed with a mixture of pig manure and nitrogen-rich co-substrates, were investigated under different organic loading rates (OLR: 1.1-5.2 g COD l-1  day-1 ), ammonia concentrations (0.2-1.5 g free ammonia nitrogen l-1 ) and stripping frequencies (3-5 times per week). The bacterial communities were dominated by Firmicutes and Bacteroidetes phyla, while the predominant methanogens were Methanosarcina sp archaea. Increasing co-substrate fraction, OLR and free ammonia nitrogen (FAN) favoured the presence of genera Ruminiclostridium, Clostridium and Tepidimicrobium and of hydrogenotrophic methanogens, mainly Methanoculleus archaea. The data indicated that the use of air-side stripping did not adversely affect thermophilic microbial communities, but indirectly modulated them by controlling FAN concentrations in the digester. These results demonstrate the viability at microbial community level of air side-stream stripping process as an adequate technology for the ammonia control during anaerobic co-digestion of nitrogen-rich substrates.

Resource recovery from pig manure via an integrated approach: A technical and economic assessment for full-scale applications.

Intensive livestock farming cannot be uncoupled from the massive production of manure, requiring adequate management to avoid environmental damage. The high carbon, nitrogen and phosphorus content of pig manure enables targeted resource recovery. Here, fifteen integrated scenarios for recovery of water, nutrients and energy are compared in terms of technical feasibility and economic viability. The recovery of refined nutrients with a higher market value and quality, i.e., (NH4)2SO4 for N and struvite for P, coincided with higher net costs, compared to basic composting. The inclusion of anaerobic digestion promoted nutrient recovery efficiency, and enabled energy recovery through electricity production. Co-digestion of the manure with carbon-rich waste streams increased electricity production, but did not result in lower process costs. Overall, key drivers for the selection of the optimal manure treatment scenario will include the market demand for more refined (vs. separated or concentrated) products, and the need for renewable electricity production.

A combination of ammonia stripping and low temperature thermal pre-treatment improves anaerobic post-digestion of the supernatant from organic fraction of municipal solid waste treatment.

Municipal Solid Waste is mostly composed of organic material which is often treated in anaerobic reactors in waste treatment plants. In most cases, the obtained digestate undergoes a solid/liquid separation step, producing a liquid fraction (known as anaerobic supernatant) rich in ammonium nitrogen that has to be further treated in order to meet discharge standards. The objective of the present work was to evaluate the feasibility of anaerobic post-digestion (37 °C) of a supernatant rich in carbon and nitrogen from a municipal waste treatment plant. In order to increase the efficiency of the process, a combined pre-treatment consisting of a low-temperature thermal process (75 °C) and ammonia stripping (1.3 Lair Lsupernatant-1 min-1) was applied. The effects of pre-treatment contact time (4 and 8 h) and the hydraulic retention time (HRT) in the anaerobic reactor (20-40 d) were studied. Supernatant pre-treatment with 8-h contact time caused 13% organic matter solubilisation, thus improving methanisation by 18% when the HRT was 40 d. At the same time, ammonia stripping allowed to maintain ammonia concentration in the digester below inhibitory values (less than 100 mg N-NH3 L-1) enabling therefore high methanogenic activity (>0.23 g COD g-1 VS d-1). The final effluent characteristics (low total ammonia nitrogen and aerobically biodegradable organic matter levels) would permit implementing subsequent less energy intensive and more environmental-friendly technologies (such as partial nitritation/anammox) to comply with discharge limits.

Enhancing thermophilic co-digestion of nitrogen-rich substrates by air side-stream stripping.

High ammonia concentrations can inhibit thermophilic anaerobic digestion, thus limiting the advantageous treatment of wastes rich both in carbon and nitrogen. In the present paper, an air side-stream stripping column was coupled to two thermophilic digesters to control ammonia content. The effects of exposing an increasing biomass fraction to the harsh conditions inside the column (pH above 9, O2 at saturation and high T) on digester performance were tested by treating and recirculating 21% of reactor volume 3 or 5 times per week. Neither biomass/liquid separation before stripping nor addition of chemicals to control pH were required. Ammonium nitrogen concentration was lowered from 2.4 to 1.1±0.1gN-TANL-1 and from 4.5 to 2.0±0.1gN-TANL-1 without compromising process stability. The air side-stream stripping process was successfully implemented to maintain ammonia concentration below 0.6±0.1gN-NH3L-1 while boosting methane production by doubling organic (and therefore nitrogen) loading rate.

The ManureEcoMine pilot installation: advanced integration of technologies for the management of organics and nutrients in livestock waste.

Manure represents an exquisite mining opportunity for nutrient recovery (nitrogen and phosphorus), and for their reuse as renewable fertilisers. The ManureEcoMine proposes an integrated approach of technologies, operated in a pilot-scale installation treating swine manure (83.7%) and Ecofrit® (16.3%), a mix of vegetable residues. Thermophilic anaerobic digestion was performed for 150 days, the final organic loading rate was 4.6 kgCOD m-3 d-1, with a biogas production rate of 1.4 Nm3 m-3 d-1. The digester was coupled to an ammonia side-stream stripping column and a scrubbing unit for free ammonia inhibition reduction in the digester, and nitrogen recovery as ammonium sulphate. The stripped digestate was recirculated daily in the digester for 15 days (68% of the digester volume), increasing the gas production rate by 27%. Following a decanter centrifuge, the digestate liquid fraction was treated with an ultrafiltration membrane. The filtrate was fed into a struvite reactor, with a phosphorus recovery efficiency of 83% (as orthophosphate). Acidification of digestate could increment the soluble orthophosphate concentration up to four times, enhancing phosphorus enrichment in the liquid fraction and its recovery via struvite. A synergistic combination of manure processing steps was demonstrated to be technologically feasible to upgrade livestock waste into refined, concentrated fertilisers.