Simultaneous recovery of phosphorus and nitrogen from liquid digestate by vacuum membrane distillation with permeate fractional condensation

A vacuum membrane distillation(VMD)process with permeate fractional condensation on membrane downstream has been developed for simultaneous recovery of phosphorus and nitrogen from liquid digestate.The polytetrafluoroethylene(PTFE)membrane flux could reach 6000 g·m-2·h-1 with the rejection efficiency of total phosphorus(TP)over 0.99,under the condition of flowrate being 120 L·h-1 and temperature being 40°C.Membrane fouling occurred with a film of organics and microorganism deposited on the surface of the membrane.Membrane flux could be reversed after the membrane was rinsed by water.Higher feed temperature and flowrate could improve the membrane flux,while hardly affect the rejection efficiency of total phosphorus.The concentration of TP could reach 1600 mg·L-1 after membrane distillation,which is about 5 times of that in initial liquid digestate.On the downstream of the membrane,some of the permeate vapor was condensed under the vacuum condition and most of water was collected here.The remaining vapor enriched with total nitrogen(TN)was compressed and pumped to the atmospheric condition to condense.The TN concentration in atmospheric condensate was as high as 7000 mg·L-1 with the process separation factor for ammonia being enhanced to 114.

DEGRADATION OF ORGANIC POLLUTANTS IN FLOCCULATED LIQUID DIGESTATE USING PHOTOCATALYTIC TITANATE NANOFIBERS: MECHANISM AND RESPONSE SURFACE OPTIMIZATION

Titanate nanofibers(TNFs)were synthesized using a hydrothermal method and were employed for the first time in this study to photocatalytically degrade organic pollutants found in flocculated liquid digestate of poultry litter.The photocatalytic performance of TNFs,with a bandgap of 3.16 eV,was tested based on degradation of organic pollutants and removal of color.Five combinations of pollutant concentration and pH were examined(0.2 to 1.3 g·L^(−1) at pH 4 to 10).Central composite design(CCD)and response surface methodology(RSM)were applied in order to optimize the removal rates of volatile fatty acids(VFA)and chemical oxygen demand(COD),and the decolorization rate.There were no significant differences between the regression models generated by the CCD/RSM and the experimental data.It was found that the optimal values for pH,dosage,VFA removal rate,COD removal rate and decolorization rate were 6.752,0.767 g·L^(−1),72.9%,59.1%and 66.8%,respectively.These findings indicates that photocatalytic TNFs have potential for the posttreatment of anaerobic digestion effluent,as well as other types of wastewater.

Effect of Biogas Digested Liquid on CH_4 and N_2O Flux in Paddy Ecosystem

Biogas production generates digested slurry as a byproduct. It can be used as a fertilizer especially after its conversion into digested liquid. A pot based study was conducted in order to evaluate the effect of the application of digested liquid on CH4 and N2O flux, and plant biomass in paddy. Analysis revealed that digested liquid treated soils released more CH4 compared to ammonium sulphate and the control. Ammonium sulphate treated soil emitted the highest N20 whereas digested liquid application decreased its emission significantly. Further, the cumulative emission over 101 d of the experiment was found to be higher for CHa （16.9 to 29.9 g m^-2） compared to N20 （-49.3 to 18.9 mg m^-2） for all treatments. Digested liquid application had positive impact on plant variables such as panicle number and weight of panicles. This study suggests that digested liquid application significantly decrease N20 emission and increase CH4 emission possibly due to affecting the availability of organic C in the soil to microbial activity for methanogenesis. Another possibility for enhancing CH4 emission by following biogas digested liquid could be attributed to the increase in plant biomass.

Control strategy of shortcut nitrification

Shortcut nitrification for ammonium-rich wastewater is energy-saving and cost-effective procedure that has become one of the hotspots in the field of biological denitrogenation. An orthogonal experiment was performed to study the combined effects of operational parameters on the performance of internal-loop airlift bioreactor for shortcut nitrification. The optimum operational parameters for the shortcut nitrification were fotmd as temperature 35 ℃, pH 8.0, dissolved oxygen concentration 1.0 mg/L, ammonium concentration 4 mmol/L and HRT 16 h, which have different influence on the performance of shortcut nitrification reactor. The pH, temperature and dissolved oxygen concentration have significant bearing on the process. The results showed that the shortcut nitrification reactor could be successfully started up within 42 d, and the reactor performance is steady with minimum NO2-/NOx- of 85.2%, maximum 93.4% and average value of 91.4% in effluent. Based on the analysis of experimental data, a new control strategy named “priority ＋ combination” for shortcut nitrification was suggested. Through this strategy, the startup and operation of shortcut nitrification for ammonium-rich sludge digester liquids were optimized. The control strategy works well to keep the reactor operation in steady state and in achieving high-efficiency for shortcut nitrification.

Effects of oxidizing environment on digestate humification and identification of substances governing the dissolved organic matter(DOM)transformation process

The formation of humic-like acids(HLAs)is an essential process for converting liquid digestate into organic soil amendments to enhance agricultural sustainability.The aim of this study was to investigate the impact of oxygen and/or MnO_(2)on the production of HLAs.Herein,abiotic humification performance of the digestate dissolved organic matter(DOM)is investigated with fluxes of air and N2 in the absence and presence of MnO_(2).Our results demonstrated that the fate of digestate DOM greatly depends on the oxidizing environment,the MnO_(2)enhanced nitrogen involved in the formation of HLAs.The synergistic effects of MnO_(2)and oxygen effectively improved the production of HLAs,and the corresponding component evolution was analyzed using spectroscopic evidence.The twodimensional correlation spectroscopy results demonstrated that the reaction sequence of digestate DOM followed the order of protein-like substances,substances with an absorbance at 325 nm,substances with UV absorbance at 254 nm and HLAs.Additionally,excitation emission matrix fluorescence combined with parallel factor analysis(EEM-PARAFAC)showed that tryptophan-like C3 was more prone to transformation than tyrosine-like C2 and was responsible for the humification process.The substance with an absorbance at 325 nm was a reaction intermediate in the transformation process of protein-like substances to HLAs.The above findings can be used to promote the production of liquid fertilizer associated with carbon sequestration as well as the sustainable development of biogas production.