Key features of successful BNR operation

Biological phosphorus removal has come of age after having been introduced with the treatment plants for the city of Johannesburg, South Africa, in 1974. There is a large number of plants in the world today and a great variety of basin configurations is used. Generally, we see excellent performance with the right wastewater characteristics and the correct design and operation, but there are still some issues not fully understood that have led to the perception that biological phosphorus removal is unreliable and unpredictable. These issues include nitrates in the feed, excessive return activated sludge recycle rates, secondary release of phosphorus and toxicity. This paper focuses on some of the issues that still frustrate designers and plant operators. There are also many claims for excellent removal by plants that appear not to conform to the established requirements for biological phosphorus removal. There is normally an explanation if the full picture is considered. The conclusion is that biological phosphorus removal is predictable and reliable if the process is properly understood.

Where is biological nutrient removal going now?

With more than 30 years of experience multiple options exist for removal of nitrogen and phosphorus from wastewater. Communities that were exempt from nutrient removal for many years must now comply with imposed nutrient limits, and in areas where technology-based nutrient limits have been in place communities are now faced with more stringent mass-based limits that are becoming more difficult to meet as their populations increase. Recent efforts in the industry have been focused on getting more out of existing plants, or in many cases where land is not available, in intensifying existing processes to increase capacity and/or level of treatment. This paper will discuss some of these methods and the general direction in which biological nutrient removal is developing to address these new challenges.

Feasibility studies and pre-design simulation of Warsaw's new wastewater treatment plant

The proposed transfer of wastewater from the western part of Warsaw, across the Wisla (Vistula) River for joint treatment at the existing eastern side "Czajka" wastewater treatment plant (WWTP) will result in combined winter flows of approx. 580,000 m3 d(-1). One-year of pilot-scale studies defined the COD characteristics and kinetics of nitrogen removal and VFA production from primary sludge. BioWin simulation was used to size and price the optional processes and pointed to the Westbank process as the most cost-effective. The process consists of a sequence of a RAS pre-denitrification zone followed by an anaerobic, anoxic and aerobic zone. Some 100-150 t d(-1) of 10% methanol would be needed to remove 2-4 mg l(-1) of NO3-N above the recommended effluent level TN = 10 mg l(-1). Applying the principle of annual average 80% TN removal, and allowing for use of daily composite samples (rather than grab) could annually save the municipality over 1.5 million Euro on external carbon source.

Impacts of reduced sulfur components on active and resting ammonia oxidizers

While there has been significant research on the nature and extent of the impact of inhibitory reduced sulfur with respect to anaerobic (e.g., methanogenic and sulfidogenic) microbial systems, only limited study has yet been conducted on the comparable effects of soluble sulfides which might occur within aerobic wastewater treatment systems. Admittedly, aerobic reactors would not normally be considered conducive to the presence of reduced sulfur constituents, but there do appear to be a number of processing scenarios under which related impacts could develop, particularly for sensitive reactions like nitrification. Indeed, the following scenarios might well involve elevated levels of reduced sulfur within an aerobic reactor environment: (1) mixed liquor recycle back through sulfide-generating anaerobic zones (e.g., in conjunction with biological nutrient removal processes, etc.), (2) high-level side-stream sulfide recycle via sludge digestion, etc., back to aerobic reactors, and (3) high-level influent sulfide inputs to wastewater treatment facilities via specific industrial, septage, etc., streams. The objective of this study was, therefore, to determine the subsequent metabolic impact of soluble sulfide under aerated and unaerated conditions, focusing in particular on ammonia-oxidizing bacteria due to their critical first-step role with nitrification. The obtained results indicated that, under catabolically active conditions, cultures of ammonia oxidizers were extremely sensitive to the presence of sulfide. At total soluble sulfide concentrations of 0.25 mg l(-1) S, active ammonia oxidation was completely inhibited. However, immediately following the removal of this soluble sulfide presence, ammonia oxidation started to recover; and it continued to improve over the next 24 h. Similar sulfide impact tests conducted with inactive ammonia oxidizers exposed during anaerobic conditions, albeit at higher dosage levels, also revealed that their subsequent aerobic activity would correspondingly be retarded. These results indicated that, after sulfide exposure under unaerated conditions, subsequent aerobic oxidative activity rates rapidly decreased as the soluble sulfide exposure was increased from 0.5 gm l(-1) S to 5 mg l(-1) S and that further reductions in this activity progressively developed as the concentration was increased to 200 mg l(-1) S. The recovery following unaerated exposure to sulfide was significantly higher at pH 7, as compared with pH 8, and although the specific nature of this variation was not established, a hypothetical explanation appeared warranted.

A review of the genus Iphimedia (Crustacea : Amphipoda) with descriptions of three new species from Australia, Papua New Guinea and Florida

Iphimedia is reviewed and a new diagnosis based on 35 known species is given. Three new species, one each from Australia, Papua New Guinea and Florida, are described. This is the only genus, in a family otherwise confined to cold and deep oceans, that has tropical species.

A review of the genus Pariphimedia (Crustacea : Amphipoda : Iphimediidae) with redescription of two species from the Southern Ocean

Two of the three species of Pariphimedia, from Antarctica, are redescribed as based on fresh material. A new generic diagnosis and a key to the species are provided.