Phosphorus removal from agricultural wastewater streams is an important aspect of managing surface water quality, due to the contribution of phosphorus to eutrophication. Removal of phosphorus through struvite precipitation allows for its recovery as a potential fertilizer, and by determining the best conditions for struvite precipitation the removal process can be optimized. The effects of pH, Mg:P ratio, and time on struvite precipitation from anaerobically digested swine manure effluent were investigated. Effluent with Mg:P ratios from 1.0:1 to 1.6:1 were adjusted to pH values between 7.5 and 9.5 and left to equilibrate for 24 h. Results indicate that phosphorus removal increased with increasing pH and Mg:P ratio; the maximum phosphorus removal achieved was 80% at pH 9.0 and a Mg:P ratio of 1.6:1. The purest struvite precipitate was found at pH 7.5, with calcium carbonate and struvite precipitating at higher pH values. A continuously stirred batch of centrate was adjusted to pH 8.4 to determine the struvite formation rate constant. The rate constant was found to be 1.55 h(-1), with 17% phosphorus removal during the first 20 min. The results indicate that struvite precipitation could be a viable method of phosphorus removal from anaerobically digested swine manure.

In order to effectively use microbial-based strategies to manage anaerobic digesters, it is necessary to distinguish between community shifts that are part of the natural dynamic of the system and shifts caused by environmental or operational disturbances. The objective of this research study was to evaluate the significance of changes in the microbial community of anaerobic digesters during failure in correlation to operational parameters such as an organic acid overload. Five continuously stirred 0.5 L reactors were set-up as semi-continuously-fed, mesophilic dairy manure digesters with a 30-day hydraulic retention time. After a 120-day stabilization period, two digesters were kept as controls, while the organic loading rates in the triplicate set were increased step-wise to ultimately provide a shock-load leading to failure using propionic acid spikes. Acidosis resulting in near cessation of biogas and termination of methane production occurred between 4 and 7 weeks, after which all the digesters continued to be fed only dairy manure. The shock loading of propionic acid led to an accumulation of mainly acetate and propionate, with low levels of iso-butyrate, butyrate, iso-valerate, and valerate. High-throughput Illumina sequencing of the V4 region of the bacterial and archaeal 16S rRNA gene in digester samples showed a significant change in the microbial community composition during propionic acid overload, followed by a return to the original composition with regular feedstock. Bacterial genera whose relative abundance decreased during the inhibition stage included Sedimentibacter, Syntrophomonas, TSCOR003.O20, and Marinilabiaceae, while the relative abundance of Lachnospiraceae, Ruminococcus, Mogibacteriaceae, Pyramidobacter, and Bacteroides increased. The relative abundance of dominant methanogens, Methanosarcina and Methanobacterium, although initially resistant, were decreased (from 91.71 to 12.14% and from 2.98 to 0.73%, respectively) during inhibition, while Methanobrevibacter and Methanosphaera that were prominent in the manure feedstock increased from 17.36 to 79.45% and from 0.14 to 1.12%, respectively. Shifts in bacterial and archaeal compositions, back to their pre-shock steady state after failure, highlight the digester’s microbial resilience and recovery potential.

Abstract. This study evaluated how feedstock with added copper sulfate (commonly used as an antimicrobial footbath solution in livestock operations) changed the performance and microbial populations of a dairy manure digester. High-throughput Illumina sequencing of the V4 region of the bacterial and the V6-V8 regions of the archaeal 16S rRNA gene in digester samples showed a significant change in the microbial community composition during addition of feedstock with copper sulfate, followed by a return to the original composition with regular feedstock. Bacterial genera that were suppressed during the inhibition period included Cloacamonas, Syntrophomonas, Butyrivibrio, and Caldicoprobacter, while the relative abundance of Acholeplasma, Desulfobulbus, Aminobacterium, Treponema, and YRC22 peaked. The dominant methanogen Methanosarcina, although initially resistant, was suppressed during inhibition, while Methanobrevibacter and Methanosphaera, prominent feedstock genera, increased. The return of the bacterial and archaeal communities to compositions similar to their previous steady states after inhibition highlights the digester’s microbial resilience and recovery potential. Keywords: . Anaerobic digestion, Copper sulfate inhibition, Illumina sequencing, Manure, Methanogens, Microbial populations, Microbiome.

2014.Phosphorus removal from solids separated hog manure by air stripping. Canadian Biosystems Engineering/Le génie des biosystèmes au Canada 56: 6.13-6.20. Removal of phosphorus (P) from hog manure can be accomplished by struvite (MgNH 4 PO 4 ) precipitation but the use of liquid hog manure in most reactors is hindered by manure total solids (TS), low soluble P concentration and interfering ions such as calcium (Ca). In addition, the cost of typical alkali and magnesium (Mg) additions adds significantly to reactor operational costs. Anaerobic fermentation can increase acidity of liquid manures by increasing both VFA and carbonic acid content. This pretreatment increases soluble P by dissolving P solids in the acid environment and also enables pH increase by air stripping CO 2 and carbonic acid. Manure solids separation technologies such as a centrifuge or rotary press produce a liquid stream with TS of <1% however, dissolved Ca can be high, producing a nonsettling floc instead of struvite crystals. On a commercial pig farm with anaerobic manure storage, a rotary press provided the liquid feed stream for a 230 L airsparged upflow struvite reactor (Crystaphos™). The reactor was airsparged to increase the pH of the liquid from 6.59 to 6.81 and no chemical additions of alkali or Mg were made in the ten trial runs conducted. Influent liquid had dissolved nutrient concentrations of 202, 174 and 217 mg/L soluble P (PO 4 ), Mg and Ca, respectively. Aeration rates were varied for different trials which affected pH increase and total phosphorus (TP) removal which averaged 32% PO 4 and 31% TP removal for 3 trials of 24 hrs each. Air stripping did not increase pH as much as expected, with an average increase of 0.25 pH units (range of 0.07 to 0.94 pH units). This was attributed to the buffering effect of manure alkalinity of 6 g/L and a volatile fatty acid (VFA) concentration of 8 g/L. This data is significant due to the significant TP reduction from a relatively small pH increase at low reactor pH conditions.Comparison of influent and effluent nutrient concentrations indicated a 1:1 molar reduction in Mg and PO4-P and the dried precipitate consisted of 85% pure struvite. Precipitate impurities were organic solids and not Ca, due to the precipitation point being low. Struvite crystals harvested from the reactor were up to 200 µm in size and no increase was found from longer reactor runs. Although TP removal was moderate, this system could be used as a second stage reduction of TP before land application. It is also apparent that struvite can form even though the manure influent is high in Ca due to the precipitation point being at a low pH. Small operational modifications such as settling tanks and dry precipitate screening would improve recovery and struvite purity.

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