Characteristics and mechanisms of phosphate adsorption on dewatered alum sludge

Water Science and Technology

Wang³

et al. 2011

This study examined a novel reuse of alum sludge, an inescapable by-product of drinking water treatment process when aluminium salt is added as a coagulant, as the main medium in a laboratory-scale multi-stage constructed wetland (CW) system for reject water treatment. Such reject water is a main concern in municipal wastewater treatment plant (MWWTP) for increasing the organic and nutrient loading. A ‘tidal flow’ strategy was employed to enhance the wetland aeration to stimulate organic matters (OM) and ammoniacal-nitrogen (N) oxidation while the ‘step feed’ operation was adopted to supply the necessary amount of carbon source for denitrification. The results reveal that alum sludge acting as P adsorbent can secure the P removal. Meanwhile, high removals of N and OM can also be obtained due to the active bacteria growth on the alum sludge surface. The results show that average removal efficiencies of 65.4 ± 12.3% for chemical oxygen demand (COD), 67.8 ± 9.2% for five-day biochemical oxygen demand (BOD5), 33.6 ± 17.0% for N and 99.5 ± 0.49% for P can be achieved over a period of 190 days. This indicates that novel reuse of alum sludge as medium in CW system can provide a promising approach for reject water treatment. Therefore, it will significantly reduce the amount of pollutant feedback through reject water recycling in a MWWTP.

Section: Discussionmentioning

confidence: 99%

A promising approach of reject water treatment using a tidal flow constructed wetland system employing alum sludge as main substrate

Yang

Water Science and Technology

Wang³

et al. 2011

“…The huge increase in P concentration in the used Al-WTR attests to the high P 303 adsorption capacity of the Al-WTR. In our previous studies, it was shown that Al-WTR has a 304 preferential adsorption for P (Yang et al 2006) and the adsorption capacity of the Al-WTR can 305 range from 10.2 mg-P/g to 31.9 mg-P/g (determined using the Langmuir adsorption isotherm) 306 (Babatunde, 2007). 307…”

mentioning

confidence: 99%

Leachability and leaching patterns from aluminium-based water treatment residual used as media in laboratory-scale engineered wetlands

Babatunde

2010

Environ Sci Pollut Res

35 Concept and purpose 36Virtually all water treatment facilities worldwide generate an enormous amount of water treatment 37 residual (WTR) solids for which environmentally-friendly end-use options are continually being 38 sought as opposed to their landfilling. Aluminium-based WTR (Al-WTR) can offer huge benefits 39 particularly for phosphorus (P) removal and biofilm attachment when used as media in engineered 40 wetlands. However, potential environmental risks that may arise from the leaching out of its 41 constituents must be properly evaluated before such reuse can be assured. This paper presents 42 results of an assessment carried out to monitor and examine the leachability and leaching patterns of 43 the constituents of an Al-WTR used as media in laboratory scale engineered wetland systems. 44 Main features, materials and methods 45Al-WTR was used as media in four different configurations of laboratory scale engineered wetland 46 systems treating agricultural wastewater. Selected metal levels were determined in the Al-WTR 47 prior to being used while levels of total and dissolved concentration for the metals were monitored 48 in the influent and effluent samples. The increase or decrease of these metals in the used Al-WTR 49 and their potential for leaching were determined. Leached metal levels in the effluents were 50 compared with relevant environmental quality standards to ascertain if they pose considerable risks. 51 Results 52Aluminium, arsenic, iron, lead, and manganese were leached into the treated effluent, but 53 aluminium exhibited the least leaching potential relative to the initial content in the fresh Al-WTR. 54Levels of P increased from 0.13 mg-P/g (fresh Al-WTR) to 33.9 mg-P/g -40.6 mg-P/g (used Al-55 WTR). Dissolved levels of lead and arsenic (except on one instance) were below the prescribed 56 limits for discharge. However, total and dissolved levels of aluminium were in most cases above the 57 prescribed limits for discharge, especially at the beginning of the experiments. 58 Conclusions, recommendations and perspectives 59Overall, the study indicate that when Al-WTR is beneficially reused for enhanced P removal in 60 engineered wetlands as opposed to landfilling it, the leaching out of aluminium into the treated 61 3 effluent beyond the prescribed limits of 0.2mg/l may be a potential problem. However, since the 62 results obtained indicate that most of the aluminium leached out are associated with solids, a post-63 treatment unit which can further reduce the level of aluminium in the treated effluent by filtering 64 out the solids could serve to mitigate this. Notwithstanding, the use of Al-WTR as a media in 65 engineered wetlands can serve to greatly enhance the removal of P from wastewaters and also serve 66 as support material for biofilm attachment.

“…This is unusual in conventional CWs as initial P removal is generally poor due to the poor P adsorption capacity of the gravel or other media used, and the fact that the other P removal mechanisms, such as biomass and plant uptake may take several months before they can significantly contribute to P removal. However, the dewatered alum sludge cake used herein is mainly composed of aluminium ions and this facilitates its ability to enhance P removal from wastewater through ligand exchange (Yang et al, 2006). Interestingly, the mean level of dissolved aluminium (Al) monitored in the effluent from the system was 0.04  0.01 mg/l and this is well below the discharge limit of 0.2 mg/l for Al discharge into all waters.…”

Section: Overall Treatment Performancementioning

confidence: 99%

Two strategies for improving animal farm wastewater treatment in reed beds

Babatunde

Environmental Technology

2010

In this study, dewatered alum sludge cakes were used as substrate in a laboratory scale tidal vertical flow reed bed system treating animal farm wastewater. The "tidal flow" operation was employed to enhance oxygen transfer into the reed bed system, while dewatered alum sludge cake was used to enhance phosphorus (P) removal in the system through ligand exchange. Except for the removal of P which was consistently high throughout the experiment, the removal of organics