Influence Of Organic Matters On Phosphorus Recovery From Wastewater By Struvite Method

Phosphorus is a kind of non-renewable and reserves limited nonmetal resource.Phosphorus recovery from wastewater is an important way of phosphorus resources recycling.Struvite (magnesium ammonium phosphate) crystallization recovering phosphorus fromwastewater is widely recognized. Organic matter is an important component of wastewatersystem whose coexisting impurity is complex. Research about the influence and mechanismof organic matter on struvite crystallization has not been reported. It is difficult to identify theinfluence of organic matters on phosphorus recovery by struvite method in the actualwastewater because of its complex composition. According to organic composition of theactual wastewater, three kinds of organic matters (protein (BSA), carbohydrate (glucose), HA)were used for preparation of simulation wastewater to investigate the influence of phosphorusrecovery by struvite method. And it also recovered phosphorus from actual wastewater at lastin this paper. The research contents and results are as follows:Firstly, the influence of concentration of organic matters on phosphorus recovery bystruvite method was investigated. Results showed that:(1) Residual phosphorusconcentration of supernatant fluid all increased with the increasing of three kinds of organicmatters. When the concentration of BSA and glucose were increased to1000mg/L, residualphosphorus concentration respectively increased from7.14mg/L of blank test to8.8mg/Land9.8mg/L. When the concentration of HA was increased to200mg/L, residualphosphorus concentration increased to14.9mg/L.(2) The purity of struvite decreased withthe increasing of concentration of BSA and HA, but didn’t changed in the presence of glucose.(3) All of the organic matters affected the crystal form. With the increasing of concentrationof BSA, crystals changed from needle shape into X-shape, feather shape and triangular prismshape. With the increasing of concentration of HA, crystals changed into feather shape. Withthe increasing of concentration of glucose, crystals changed into stick shape and needle shapemixture.(4) The particle size of crystals reduced in the presence of three kinds of organicmatters. When the concentration of BSA, HA and glucose was increased to200mg/L,crystals particle size respectively reduced from17.7μm to11.2,12.7and16.3μm.Secondly, the influence of aging time on phosphorus recovery by struvite method in thepresence of organic matters of fixed concentration was investigated. Results showed that:(1) Residual phosphorus concentration significantly first decreased and then increased with theincreasing of aging time in the blank test, as well as in the BSA and glucose additionexperiments. Residual phosphorus concentration first decreased and then remainedunchanged in HA addition experiment.(2) It was known that crystals changed from theneedle shape into dendritic shape in the blank and glucose addition experiments contrastingthe aging time of1and10days. The aging time almost didn’t affect the crystals in the HAand BSA addition experiments.(3) The crystals particle size increased first and thendecreased with the increasing of aging time in the blank test. The variation of BSA andglucose addition experiments were the same to the blank test, and their particle sizerespectively reached19.7and27.5μm. The crystals particle size increased first and thenremained unchanged with the increasing of aging time in HA addition experiment.(4) Thegrowth rates of crystals were1.24,1.02and1.21μm/d between1~10days of aging time inthe blank, BSA and glucose addition experiments. But the crystal particle size only increased0.8μm in30days in the HA addition experiments.(5) Results of TOC and Mg/P molar ratioanalysis showed that struvite crystals surface adsorption of complexes formed by organicmatters and Mg2+. And analysises of crystal shape and particle size showed that thecomplexes inhibited struvite crystal growth. The glucose didn’t participate in reaction byadsorption.Thirdly, the influence of Mg/P on phosphorus recovery by struvite method in thepresence of organic matters of fixed concentration was investigated. Results showed that:(1)The residual phosphorus concentration significantly first decreased fast and then remainedunchanged with the increasing of Mg/P in the blank test, as well as in the BSA, glucose andHA addition experiments. The influence sequence of organic matters on phosphorus recoverywas as follows: HA＞BSA＞glucose＞blank.(2) The purity of crystals reduced with theincreasing of Mg/P in the blank test, as well as in the glucose addition experiments. But thepurity fluctuated above and below90%in the HA and BSA addition experiments.(3) Thecrystals changed into "coral shape" with the increasing of Mg/P in the blank test, as well as inglucose and HA addition experiments. But the crystals changed into flaky shape in the BSAaddition experiment.(4) Comprehensive consideration of the phosphorus and struvite purity,M/P ratio should be controlled at1.4in actual recovery process.At last, the influence of struvite method recovering phosphorus from sludge anaerobicwastewater was investigated. Results showed that:(1) Release effect of nitrogen andphosphorus which was treated by ultrasonic joint acid (pH5) and stirring treatments was best.The release quantity of NH3-N and PO43--P respectively reached223mg/L and144.9mg/L.(2) Purity of struvite recovered from sludge anaerobic supernatant fluid without Ca2+onlyreached88.6%, and phosphorus recovery rate reached97.2%.