Bench-scale study on zero excess activated sludge production process coupled with ozonation unit in membrane bioreactor

Abstract

In this bench-scale study, two promising processes for minimizing excess activated sludge (EAS) production, i.e., membrane bioreactor (MBR) and sludge ozonation (SO), were coupled in this study into the MBR-SO process to treat domestic wastewater for 80 days, and the vital related operational factors were also investigated. Mathematical models were developed to elucidate the relationships among process control parameters and the actually operational effects of these parameters on the performance of MBR-SO process. As a consequence, the ratio of flow-rate draining to ozonation unit (q) to influent wastewater flow-rate (Q) was the mainly operational parameter, which was significantly affected by the sludge lysing ratio in ozonation unit (xi), produced COD per unit mass lysed MLSS (eta), observed sludge yield coefficient for wastewater (Y(obs)) and intrinsic yield coefficient for COD produced by lysed sludge (Y(2)). To keep the mixed liquid suspended solid concentration (MLSS) in MBR around 8,000 mg/L, the ratio of q/Q and xi for each batch ozonation was set at 0.0067 and 0.72, respectively. The generated EAS was continuously drained into ozonation unit at a frequency of 2 batch/d for lysing cells, and almost constant MLSS concentration with zero observed sludge yield coefficient (Y(obs)) and excellent effluent quality could be achieved in MBR except for TP concentration (only approximately 3.62% TP removal efficiency rate obtained in Test stage). The calculation of sludge disintegration number (SDN) and the maximum SDN (SDN(max)) indicated that the higher xi could reduce apparently the sludge amount needed for ozonation. The low input ozone gas concentration and high flow-rate could enhance the sludge lysing effects at same ozone dosage, and therefore lower energy consumption of 0.041Yuan (USD 0.0053)/m(3) wastewater was obtained. Overall, mass balance showed that the preset value of operation parameters listed in mathematical models matched well with trends of sludge reduction found in this experimental result.

A fundamental analysis of continuous flow bioreactor and membrane reactor models with non‐competitive product inhibition. II. Exponential inhibition

“…[7] In this paper, we extend our earlier investigation by employing the second of these expressions. In the discussion section, we compare the results obtained in our earlier investigation [7] using expression (2) with those obtained in the current investigation using expression (2). Equation (2) was first used by by Aiba et al .…”

“…When β = 0 the model equations provide a simple representation of an idealised membrane reactor. [1,2] The case (0 < β < 1) represents a number of reactor configurations. These include: a non-idealised membrane reactor, in which some of the microorganisms leave the reactor vessel in the effluent stream; a fixed-bed biological process with a large recirculation rate and with biomass detachment -β is the fraction of the biomass that is detached from the reactor by the flow [Ref.…”

“…These include [Ref. [6], p. 179] µ(S , P ) = µ(S ) · exp − P K p (2) µ(S , P ) = µ(S ) · 1 − P P m H(P m − P ) (3) In these expressions µ(S ) is the growth rate expression in the absence of product, K p is the product inhibition constant, P m is a concentration at which growth stops and H is the Heaviside function. The third of these expressions can be derived as a Taylor series expansion of the second for small product concentrations.…”

A Mathematical Analysis of a Membrane Bioreactor Containing a Sludge Disintegration System

“…This approach works primarily by disintegrating bacterial cell walls. A variety of methods have been used in the literature to achieve this aim including: the addition of anoxic/anaerobic stages (Barker & Dold, 1996;Yoon, 2003), enzyme treatment (Barjenbruch & Kopplow, 2003), freezing and thawing (Chu et al, 1999), the use of an inclined-plate membrane bioreactor (Xing et al, 2006), ozonation (Yasui et al, 1996;Sakai et al, 1997;Egemen et al, 2001;Song et al, 2003;Wang et al, 2008), ozonation combined with chemical treatment (Oh el al, 2007), thermal treatment (Goma et al, 1997;Kepp et al, 1999), and ultrasound (Yoon et al, 2004b). Combinations of these treatments are also possible.…”

An analysis of an activated sludge process containing a sludge disintegration system

“…Methods that have been investigated to reduce excess sludge production include the addition of anoxic/anaerobic stages [Barker and Dold (1996); Yoon (2003)], enzyme treatment [Barjenbruch and Kopplow (2003)], freezing and thawing [Chi et al ( 1999)], an inclined-plate membrane bioreactor [Xing et al (2006)], ozonation [Yasui et al (1996); Sakai et al (1997); Egemen et al (2001); Song et al (2003); Wang et al ( 2008)], ozonation combined with chemical treatment [Oh et al (2007)], thermal treatment [Goma et al (1997); Kepp et al ( 1999)], and ultrasound [Yoon (2004)].…”