Recovery of phosphorus and nitrogen from human urine by struvite precipitation, air stripping and acid scrubbing: A pilot study.

Sustainable and closed-loop nutrient cycling require the recovery of valuable resources from wastewater. Resource recovery from diluted wastewater streams is limited by diluted concentrations and unfavorable reaction kinetics. In comparison, source separated urine allows resource recovery from a highly concentrated nutrient stream, resulting in a more sustainable and efficient recovery practice. Different nutrient recovery methods from urine have been studied in lab-scale, but pilot or full-scale process evaluations remain sparse. In this study, recovery of struvite and ammonium sulfate from urine of pregnant women was demonstrated at a pilot-scale treatment facility by means of precipitation and air stripping/acid scrubbing. The system achieved 94% struvite precipitation efficiency but merely 55% of the crystals were removed and recovered. The low phosphorus recovery was due to the washout of small crystals that escaped the sieve and settling tank, hence requiring an improved method for crystals capture. The removal and recovery efficiencies for nitrogen were 93% and 85%, respectively. Composition analysis of the produced fertilizers indicated that struvite was the dominated precipitate and quality of the ammonium sulfate met European standards. Carbamazepine and diclofenac were added in the urine to measure the fate of pharmaceuticals in the treatment system. Very little of the spiked pharmaceuticals (<0.01%) accumulated in the produced struvite and ammonium sulfate. The overall energy demand of the pilot system was 1066 MJ per m3 urine processed or 198 MJ per kg N removed. Energy efficiency was not optimized and can be improved in many ways.

Varus alignment leads to increased forces in the anterior cruciate ligament.

BACKGROUND: Varus thrust of the knee is a dynamic increase of an often preexisting varus angle and it is suspected to be a major reason for failure of anterior cruciate ligament reconstructions. However, it is not known if a direct relationship exists between varus thrust and forces in the anterior cruciate ligament. HYPOTHESIS: Forces in the anterior cruciate ligament increase with increasing varus alignment, and consequently an anterior cruciate ligament deficiency in a varus-aligned leg leads to more lateral tibiofemoral joint opening. STUDY DESIGN: Controlled laboratory study. METHODS: Six human cadaver legs were axially loaded with 3 different weightbearing lines--a neutral weightbearing line, a weightbearing line that passes through the middle of the medial tibial plateau (50% varus), and a line passing the edge of the medial tibial plateau (100% varus)--that were used to create a varus moment. The resulting lateral tibiofemoral joint opening and corresponding anterior cruciate ligament tension were measured. The tests were repeated with and without the anterior cruciate ligament in place. RESULTS: In the neutral aligned legs, there was no apparent lateral joint opening, and no anterior cruciate ligament tension change was noted. The lateral joint opening increased when the weightbearing line increased from 0% to 50% to 100%. The lateral joint opening was significantly higher in 10 degrees of knee flexion compared with knee extension. In the 100% varus weightbearing line, the anterior cruciate ligament tension was significantly higher (53.9 N) compared with neutral (31 N) or the 50% weightbearing line (37.9 N). A thrust could only be observed in the 100% weightbearing line tests. In the absence of an anterior cruciate ligament, there was more lateral joint opening, although this was only significant in the 100% weightbearing line. CONCLUSION: There is a direct relationship between varus alignment and anterior cruciate ligament tension. In the absence of an anterior cruciate ligament, the amount of lateral opening tends to increase. With increasing lateral opening, a thrust can sometimes be experimentally observed. CLINICAL RELEVANCE: A varus alignment in an anterior cruciate ligament-deficient knee does not necessarily lead to a varus thrust and therefore does not always need operative varus alignment correction. However, in an unstable anterior cruciate ligament-deficient knee with a varus thrust, it might be safer to perform a high valgus tibial osteotomy to minimize the risk of an anterior cruciate ligament reconstruction failure.