This paper reviews the technology and biotechnology to remove heavy metals (such as copper, arsenic, lead and zinc) and cyanide from contaminated wastewater. The paper places special emphasis on gold mine wastewater and the use of low cost materials as sorbent. Various biological as well as physicochemical treatment processes are discussed and compared on the basis of costs, energy requirement, removal efficiency, limitations and advantages. Sorption using natural plant materials, industrial and agricultural waste has been demonstrated to have the potential to replace conventional methods for the removal of heavy metals because of its cost effectiveness, efficiency and the local availability of these materials as biosorbent. The parameters affecting sorption, such as initial ion concentration, pH, sorbent dosage, particle size and temperature, are discussed. The overall treatment cost of metal and cyanide contaminated wastewater depends on the process employed and the local conditions. In general, technical applicability, cost-effectiveness and plant simplicity are the key factors in selecting the most suitable treatment method.

Anaerobic oxidation of methane (AOM) in marine sediments is coupled to sulfate reduction (SR). AOM is mediated by distinct groups of archaea, called anaerobic methanotrophs (ANME). ANME co-exist with sulfate-reducing bacteria, which are also involved in AOM coupled SR. The microorganisms involved in AOM coupled to SR are extremely difficult to grow in vitro. Here, a novel well-mixed submerged-membrane bioreactor system is used to grow and enrich the microorganisms mediating AOM coupled to SR. Four reactors were inoculated with sediment sampled in the Eckernförde Bay (Baltic Sea) and operated at a methane and sulfate loading rate of 4.8 L L(-1) day(-1) (196 mmol L(-1) day(-1)) and 3.0 mmol L(-1) day(-1). Two bioreactors were controlled at 15 degrees C and two at 30 degrees C, one reactor at 30 degrees C contained also anaerobic granular sludge. At 15 degrees C, the volumetric AOM and SR rates doubled approximately every 3.8 months. After 884 days, an enrichment culture was obtained with an AOM and SR rate of 1.0 mmol g(volatile suspended solids) (-1) day(-1) (286 micromol g(dry weight) (-1) day(-1)). No increase in AOM and SR was observed in the two bioreactors operated at 30 degrees C. The microbial community of one of the 15 degrees C reactors was analyzed. ANME-2a became the dominant archaea. This study showed that sulfate reduction with methane as electron donor is possible in well-mixed bioreactors and that the submerged-membrane bioreactor system is an excellent system to enrich slow-growing microorganisms, like methanotrophic archaea.

e Communities of anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB) grow slowly, which limits the ability to perform physiological studies. High methane partial pressure was previously successfully applied to stimulate growth, but it is not clear how different ANME subtypes and associated SRB are affected by it. Here, we report on the growth of ANME-SRB in a membrane capsule bioreactor inoculated with Eckernförde Bay sediment that combines high-pressure incubation (10.1 MPa methane) and thorough mixing (100 rpm) with complete cell retention by a 0.2-m-pore-size membrane. The results were compared to previously obtained data from an ambient-pressure (0.101 MPa methane) bioreactor inoculated with the same sediment. The rates of oxidation of labeled methane were not higher at 10.1 MPa, likely because measurements were done at ambient pressure. The subtype ANME-2a/b was abundant in both reactors, but subtype ANME-2c was enriched only at 10.1 MPa. SRB at 10.1 MPa mainly belonged to the SEEP-SRB2 and Eel-1 groups and the Desulfuromonadales and not to the typically found SEEP-SRB1 group. The increase of ANME-2a/b occurred in parallel with the increase of SEEP-SRB2, which was previously found to be associated only with ANME-2c. Our results imply that the syntrophic association is flexible and that methane pressure and sulfide concentration influence the growth of different ANME-SRB consortia. We also studied the effect of elevated methane pressure on methane production and oxidation by a mixture of methanogenic and sulfate-reducing sludge. Here, methane oxidation rates decreased and were not coupled to sulfide production, indicating trace methane oxidation during net methanogenesis and not anaerobic methane oxidation, even at a high methane partial pressure.A naerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) is a process influenced by the CH 4 partial pressure. The SR rate of sediment from Hydrate Ridge was significantly higher at an elevated CH 4 partial pressure (1, 2). At between 0 and 0.15 MPa, there was a positive linear correlation between the CH 4 partial pressure and the AOM and SR rates of an anaerobic methanotrophic enrichment obtained from Eckernförde Bay sediment (3). The rate of methane-dependent sulfide production by microbial mats from the Black Sea increased 10-to 15-fold after the methane partial pressure was increased from 0.2 to 10.0 MPa (4). The affinity constant for methane (K m ) of anaerobic methanotrophs from Gulf of Cádiz sediment is about 37 mM, which is equivalent to 3 MPa CH 4 (5). Because of the more negative Gibbs free energy change (⌬G) at elevated CH 4 partial pressures, the growth of anaerobic methanotrophs might be faster when the CH 4 partial pressure is increased (see Fig. S1 in the supplemental material). Bioreactor studies with high methane pressure have been performed (4, 5), but it is not clear how the different subtypes of communities of anaerobic methane-oxidizing archaea (ANME) and associated sulfate-reducing bacteria (SRB) are af...