The Effects Of SRT On The Characteristics Of The Biochemical Treatment System

Sludge retention time (SRT), also known as the average residence time of thebiosolids, is an important parameter for biological treatment system’s design andoperation. The effect of SRT on the biochemical treatment system related to it’s running,managing, costs, whither effluent can reach the standard and other aspects. It is theimportant parameter we must focus on related to sewage treatment system optimaloperation control, and the mentioned standard transformation. Within the scope ofaccess to the information, found that most of the research about SRT are related tonitrogen and phosphorus removal, and there is a lack of a comprehensive, systematicresearch on the effect of SRT on biological treatment systems characteristics, especiallylack of research on the effects of SRT on sludge loading, sludge yield, MLVSS/MLSSratio, the DOM in the effluent of nitrogen and phosphorus removal biological treatmentsystem. Based on the summary of the potential impact of SRT on biological treatmentsystem, theses systematically research the effacts of SRT (6d~100d) on the operationalcharacteristics of biological treatment system with the object of SBR systerm withfunction of phosphorus and nitrogen removal. The study main includes the effacts ofSRT on the running characteristics of biological treatment systems, sludgecharacteristics, effluent quality and dissolved organic matter and DOM ineffluent.Research results show that:①Under the same volume load, the longer the SRT of the system is,the MLSS ishigher, the the sludge load is lower, the apparent yield is lower, the shock loadcapability is more strong.WHen the same SRT is the same, the higher the volume load is,the higher the MLSS is, but the sludge load and the apparent yield was relatively stable,basically not affected by volume load.②Under the condition of experiment, the median diameter of the sludge flocsrange between84.34um and119.36um, volume mean diameter range between102.51um and147.50um, as the extension of SRT the average particle size shows decreasestrend, when the SRT is short, sludge floc size distribution is relatively dispersed, withthe extension of SRT the particle size distribution tends to uniform.③Within the scope of testing, sludge SVI in SBR system were less than100,sludge settling performance is good. With the increase of SRT in the system the sludgevolume index SVI decrease. In these systems MLVSS/MLSS ratios are high, and with the increase of sludge age, the value is reduced. The research found that theMLVSS/MLSS ratio at the end of the aerobic sludge is lower than sludge at the end ofanaerobic, and settling performance of sludge at the end of the aerobic sludge is betterthan sludge at the end of anaerobic, this is because in the nitrogen and phosphorusremoval biological treatment system, aerobic phosphorus uptake increase thepolyphosphaten in sludge.④From the results, when the SRT is20d, the sludge dewatering performance isthe best, the long SRT system is the second, and the short SRT is the worst The impactmechanism of SRT on sludge dewatering performance remains to be further studied.⑤When using DGGE separate PCR amplification products found that multiplebands were separated in each lane, each stripe represents a genus, it shows themicroorganisms is diversity in the SBR reactor. And the effect of SRT, sludge load onthe diversity of the population of microorganisms in the SBR system is not large, butthere is a certain degree of variation in the number of the population, and the advantagebacterium group.When the SRT is20~30d microbial species in the system are themost, from the perspective of microbial synergy principle, the more the microbialspecies are, the pollution degradation degree is better.⑥SRT have significant effects on COD removal and denitrification under testconditions, and with the increase of SRT: COD removal effect is better, the effluent canstability achieve A stander, but when the SRT extend further, because of the endogenousrespiration the COD is a little higher than the system with the20d SRT; NH3-N removaleffect is better, when STR>10d, NH3-N can achieve A standard stablily;TP removalefficiency is worse, when STR>20d, it can’t achieve the standard, but after introducingPhostrip, TP can reach level of A standard; When the SRT is10d, TN removal effect isthe best, but it needs dosing carbon source in denitrifying phase if make the TN stabilityachieving level of A standard, and dosing quantity is20~30gCOD/L.⑦Under the test conditions, domestic sewage has two significant proteinfluorescence peak, a humic acid fluorescent peak and a fulvic acid peak. Researchresults show that the microbial degradate protein significantly, with the extension ofSRT the degradation degree increasing; When SRT is greater than10d, the longer theSRT is, the humic acid fluorescence peak in effluent is higher, it shows that when SRTextension, the microbial metabolism intensify, and endogenous respiration productaccumulation significantly, which is the main reason SRT increased,then CODincreased; Peaks of fulvic acid fluorescence change little. When fitting the peak intensity of the fluorescence with the COD and TN found that relevance of the proteinfluorescence intensity of the peak A and the COD is up to0.975.Research results show that using the SRT regulate the running of biochemicalsystem is more effectively, and it is more b enefit to keep high system shock loadcapacity and stable good effluent quality.The Research is support by National Water Pollution Control and Treatment ofMajorScience and Technology projects （2013ZX07314001）.