Elsevier

Journal of Membrane Science

Volume 446, 1 November 2013, Pages 277-285
Journal of Membrane Science

Single household greywater treatment with a moving bed biofilm membrane reactor (MBBMR)

https://doi.org/10.1016/j.memsci.2013.06.049Get rights and content

Highlights

  • A moving bed biofilm membrane reactor prototype for on-site greywater achieves reuse guidelines.

  • A mandatory start-up with seed organism could not be confirmed.

  • The strong variation of the ambient temperature and loading did not remarkably influence the treated water quality.

  • Natural hair colour in greywater could be removed up to 80%.

  • The energy consumption of the treatment process was only 1.26 kW h/m³.

Abstract

A combination of moving bed biofilm reactor and membrane filtration (MBBMR) was studied for on-site greywater treatment for a single household with four inhabitants over 10 months. Synthetic greywater with different loading and varying ambient temperatures was part of the study. Although different stress situations were applied, the results of the treated effluent achieved NSF (International Standard/American National Standard) reuse guidelines. Mean flux of the membrane during permeating phase was 12.9 L/m2 h. Additionally, natural hair colour could be removed by almost 80% and energy consumption of the pilot unit was optimized during the operation to less than 1.3 kW h/m3. The process configuration proved to be feasible for the implementation on on-site microsystems with high flow and load variation.

Introduction

Greywater from showers, baths, wash basins, washing machines and kitchen is a major part of the overall household waste water with a share of up to 80% [5]. Daily amount per person can reach values of 15–55 L day−1 up to 90–120 L day−1 [18], [17]. A wide range of treatment methods of greywater can be found in literature as well as already on the market. So far low and high-tech systems such as simple coarse filtration up to multi-barrier concepts including biological treatment, membrane filtration and UV disinfection exist together and also have been applied to different building sizes [15]. An innovative and reliable technology in terms of advanced biological treatment and removal of pathogens represents the activated sludge membrane bioreactor (AS-MBR). Table 1 lists recent studies about greywater treatment with AS-MBR plants and achieved treated effluent quality. All studies show excellent removal efficiencies of organics and microorganism but feasibility in view of operational costs and estimated investment remain unclear.

AS-MBR technology is applied only for a small number of on-site sewage or greywater treatment applications for single households till now [13]. One obstacle for a broad dissemination could represent the investment and operational costs of commercially available units which are in comparison to conventional biological treatment still higher and therefore not cost-effective for small buildings [5], [7]. Other acceptance problems may result from increased maintenance due to fouling of membranes [11] and in consequence higher energy demand for fouling control caused by air scouring of membranes [16].

As a result of these disadvantages of the conventional AS-MBR systems, an alternative membrane configuration called biofilm membrane bioreactors (BF-MBR) was developed by Leiknes and Ødegaard [12]. The BF-MBR reactor is divided into two compartments. One is filled with moving bed biofilm growth bodies and the other one is equipped with the membrane modules and acts as a filtration chamber. Retained sludge is recirculated to the first chamber or removed by system by a pump. When operated with sewage, this process was shown to have higher flux rates than conventional AS-MBR probably due to lower suspended solid concentration in the bioreactor. The low suspended solid concentration may also lead to reduced clogging of membranes and less sludge accumulation in the membrane housing. Thus less fouling control is needed to maintain a high flux.

In order to reduce investment and operational costs of small onsite MBR plants for greywater treatment, the authors of this study combined a moving bed biofilm reactor and membrane filtration system in one tank. The system was operated for 10 months with synthetic low and high strength greywater. This new configuration should combine the advantage of high effluent quality and low space requirements of AS-MBR and the lower operational costs of the BF-MBR. The combined process was named moving bed biofilm membrane reactor (MBBMR). This study describes the performance of this reactor type on a single-household scale and presents operational aspects and costs as well. The results of 10 months operation show that the treated effluent of the combined process configuration meets international reuse guidelines and energy demand could be lowered to less than 1.3 kW h/m³.

Section snippets

Pilot plant set-up

A moving bed biofilm membrane reactor (MBBMR) was studied for a four person's household treating 200 L greywater per day. Fig. 1 shows the process flow scheme of the MBBMR pilot plant. The moving bed biofilm bioreactor and the membrane filtration unit were placed in the same tank with a capacity of 350 L which also included sufficient balancing volume for incoming greywater flushes. In low level this tank still had a volume of 110 L. As moving bed, cylindrical biomass carriers (d=36 mm, h=20 mm)

Treatment performance of bioreactor

The MBBMR pilot unit with a capacity of four people equivalent (200 L/day) was tested for 10 months with synthetic greywater. Different operational conditions and stress situations typical for single households were simulated in order to verify the performance of the process. This included a start-up with and without seed microorganism, high and low influent COD loadings, and a seasonal change of ambient temperatures during the year, restarting after vacation and the loading with natural hair

Conclusion

A combination of a moving bed biofilm reactor and membrane filtration in one reactor (MBBMR) which treated 10 months greywater with different loads and temperature simulating a single household achieved renowned international effluent reuse guidelines. A start-up with seed organism was not advantageous concerning degradation performance or membrane fouling. The strong variation of the ambient temperature and loading did not remarkably influence the treated water quality. Natural colour in

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