Recovery of Nitrogen and Phosphorous as Struvite From Swine Waste Biogas Digester Effluent

Objective To investigate the feasibility of nitrogen and phosphorus recovery from swine waste biogas digester effluent and the effects of pH and NH4^＋： Mg2^＋： PO4^3- molar ratio on its precipitation. Methods Precipitation experiments with swine waste biogas digester effluent were conducted at pH 7.5, 8.0, 8.5, and 9.0 together with NH4^＋： Mg^2＋： PO4^3- molar ratios 1： 0.2： 0.08, 1： 1： 1, and 1： 1.5： 1.5. Chemical and X-ray diffraction （XRD） analysis were done to determine the composition of the precipitate. Results The highest removal and recovery of NH4^＋ and PO4^3- were achieved at pH 9.0 in each experiment. The elevation of pH to 9.0 alone could decrease the initial PO4^3- concentration from 42 mg L^-1 to 4.7 mg L-1 and 89.2% PO4^3- recovery was achieved. The pH-molar ratio combination 9.0-1： 1.5： 1.5 effected 76.5% NH4^＋ and 68.5% PO4^3- recovery. The molar ratio of 1： 1： 1 together with pH elevation to 9.0 was determined to be the optimum combination for both NH4＋ and PO4^3- removal as it recovered over 70% and 97% of the initial NH4^＋ and PO4^3-, respectively. Conclusions Nitrogen and phosphorus can be recovered from biogas digester effluent as struvite.

The current phosphate recycling situation in China and Germany:a comparative review

Phosphorus(P)is an indispensable element for organisms but the primary source of P-mineral phosphate resources-are non-renewable.Agricultural production has a high demand for fossil phosphate resources,but the resulting phosphate-rich residues are lack of management.This leads to rapid reserves depletion and severe phosphate pollution risks.One sustainable way is to reuse the phosphate dispersed in various residues such as sewage sludge and livestock manure.Diverse techniques have emerged to recover phosphate from wastes to close the phosphate cycle.While it is a global issue,the regional situations regarding potential phosphate scarcity and its management differ strongly.China is rich in phosphate resources,but over-exploitation has greatly increased the risk of phosphate rocks depletion,while in Germany the P resources depend on imports,but there is commitment to keep a balance between import and utilization.This had led to great differences in the way the two countries deal with the"re-use"of phosphate in waste.China is now in a transition phase from the simple terminal pollution control to"waste"reuse and nutrient resources recycling.One sign of this tendency is the mandatory garbage classification and preparation for further processing and recycling.This was first implemented in Shanghai in 2019,whereas Germany has been following the legal framework for waste management since the 19 th century.There are a series of laws to control the nutrient loss from municipal and agricultural activities,as for instance with sewage sludge ordinance and fertilizer legislation.Many of these laws have been newly revised recently.Sewage sludge cannot be directly utilized on farmland as organic fertilizer any more.Alternatively,phosphate and other nutrients should be recovered from sewage sludge.Advanced phosphate recovery technologies and related nutrient recycling schemes are proceeding.This review summarizes the current situation of phosphate-containing residues management and phosphate reuse in China and Germany.The state legislation and policies,which would affect the phosphate recycling concept are presented as well.As there are various kinds of phosphate-containing residues,different phosphate recovery technologies can be applied.Those technologies are discussed from their mechanism and suitability.