Domestic wastewater sludge valorization: Multi-criteria evaluation of anaerobic digestion vs. hydrothermal liquefaction.

The emerging hydrothermal liquefaction (HTL) process is evaluated against the classical anaerobic digestion (AD) processes for stabilizing wastewater sludges and recovering their energy- and nutrient-contents. Although HTL affords faster stabilization, better process stability, and liquid fuel and sterile fertilizer recovery, it suffers from higher energy demand and lower technology readiness level. For a rational comparison of these pathways, a multi-criteria evaluation is conducted considering 21 technical, environmental, economic, and social criteria. Criteria values for the HTL-pathway were derived from laboratory tests while those for the AD-pathway were compiled from literature. Of the 16 process alternatives evaluated, the AD-pathway including nitrogen-recovery by air-stripping and phosphorus recovery by the MEPHREC® process ranked first followed by the HTL-pathway. This multi-criteria study suggests that the HTL-pathway could be engineered as a superior alternative for sludge stabilization and resource recovery if phosphorus recovery and its technology readiness level could be improved.

Feasibility of ammonium sulfate recovery from wastewater sludges: Hydrothermal liquefaction pathway vs. anaerobic digestion pathway.

This study evaluated two pathways to recover the nitrogen-content of wastewater sludges as ammonium sulfate (AmS) for use as fertilizer. The first pathway entails sludge stabilization by hydrothermal liquefaction (HTL) followed by recovery of AmS from the resulting aqueous product by gas permeable membrane (GPM) separation. The second one entails stabilization of the sludges by anaerobic digestion (AD) followed by recovery of AmS from the resulting centrate by GPM separation. A bench-scale GPM reactor is shown to be capable of recovering >90% of N in the feed. Recoveries of NH3-N in the HTL-pathway ranged 96-100% in 5.5-7.5 h at mass removal rates of 0.2-0.3 g N/day, yielding 3.3-6.0 g AmS/L of feed. Recoveries of 98% were noted in the AD-pathway in 4 h at mass removal rates of 0.06-0.97 g N/day and a yield of 1.7-2.1 g AmS/L of feed. Inductively coupled plasma optical emission spectrometer analysis confirmed that both pathways yielded AmS meeting the US EPA and European region guidelines for land application. The GPM reactor enabled higher nitrogen-recoveries in the HTL-pathway than those reported for current practice of AD followed by ammonia stripping, ion exchange, reverse osmosis, and/or struvite precipitation (96-100% vs. 50-90%). A process model for the GPM reactor is validated using performance data on three different feedstocks.

Posthatch carbohydrate feeding and subsequent performance of turkey poults.

In two floor pen trials, day-old poults were fed a low-protein (18.6%) diet for the first 24 or 48 h compared with control poults fed a 28% protein diet. Beyond these initial treatments, all poults were treated identically and were fed the normal progression of starter, grower, and finisher diets to market weight. The treatments did not alter market age body weight or feed conversion. Early mortality and feed intake during the first 48 h were unaffected by the treatments. Feeding the low-protein diet for 24 h enhanced liver glycogen reserves compared with the control. In a battery cage trial, diets containing 50, 33, or 15% available carbohydrate (20, 28, or 35% crude protein, respectively) were fed for 24 h posthatch. The diets had no effect on blood glucose level, but liver glycogen concentration increased with increasing dietary carbohydrate. The results clearly indicate that carbohydrate metabolism is altered by posthatch dietary carbohydrate level. The results also suggest that the dietary protein requirement during the first 24 or 48 h posthatch may not be as high as it is currently thought to be.

Effect of three routes of spectinomycin injection in neonatal turkeys with mixed bacterial contamination.

Neonatal poults diagnosed to have mixed bacterial contamination were injected with spectinomycin in one of three different routes: yolk sac, intramuscularly, or subcutaneously. An additional group was uninjected controls. Yolk sac injections, but not other routes, resulted in significantly heavier birds.